docs: mark M8 done

docs/ROADMAP.md

@@ -10,18 +10,20 @@ Status legend: ✅ done · 🚧 in progress · ⬜ not started
 
 ## Current state (one line)
 
-✅ **M7 done.** The Stopwatch tab is real: start, pause and reset, a readout to
-hundredths whose fraction is drawn smaller than its seconds, laps with their
-split and their running total newest-first with the fastest and slowest marked,
-the lap in progress as its own counting row, and a silent `specialUse`
-foreground service whose Lap and Pause work with the app closed — its ticking
-drawn by the system, so it costs no battery to keep accurate. A stopwatch that
-meets a reboot comes back **paused at what it banked**, with every lap intact,
-rather than inventing the time it lost; a clock change cannot move it at all.
-M0's promise that the big-readout typography would be settled against a working
-stopwatch is kept, and every readout in the app now sits in fixed columns. One
-tab is still an empty state: **M8** (world clock — the zone list, ICU names,
-offsets and the analog face) is next.
+✅ **M8 done.** The World clock tab is real, and **every tab now has its own
+content** — no empty state is left anywhere in the app. A hero analog face shows
+your home zone, and its dial morphs between a circle and a sun with the hour
+there, so a glance answers "is it the middle of the night" without a line of
+text saying so — the app's one deliberate `MaterialShapes` showpiece, spent on
+information rather than decoration. Cities come from the device's own tzdata,
+named and localised through ICU behind a seam, searched by word-prefix over
+folded text so ASCII finds São Paulo; each row carries its time, its offset and
+its day difference **relative to home**, all read at the instant so both sides
+of a daylight-saving change are right on the day. The list reorders by drag or
+by a move-up/move-down action a screen reader can reach, and the home zone is
+set by hand or left following the device. **M9** (system interop — the full
+`android.provider.AlarmClock` contract and its hostile-input validation) is
+next.
 
 ---
 
@@ -411,12 +413,84 @@ M7 owns only how the paused result is presented.
   the gate but have **never run on hardware**, as no device was attached — the
   same caveat M5's seven and M6's four carry.
 
-### ⬜ M8 — World clock
+### ✅ M8 — World clock
 IANA zone list with search, ICU-localised city and zone display names, offset and
 day-difference relative to home, reorder, home-zone handling. The analog face
 built from `MaterialShapes` / `androidx.graphics.shapes` — the app's one
 deliberate showpiece.
 
+  ✅ 1 139 JVM tests, 171 of them new, and **still no Robolectric** — kept now
+  for a fourth screen, and this was the milestone most tempted to break it,
+  because ICU and `Canvas` both look like they need a device. They do not:
+  everything ICU answers is behind `ZoneNames` (faked, with per-method call
+  counters and a `failEverything` flag), everything the face draws is
+  `DrawScope` calls over `AnalogFace`'s angles and `DayNight`'s fraction — two
+  pure objects asserted at every minute of the day without a pixel — and
+  everything the list and the picker decide is `WorldClockRows`,
+  `ZonePickerRows`, `ZoneSearch`, `ZoneComparisons`, `ZoneCatalog` and
+  `WorldClocks`. Every write is a `WorldClockViewModel` method over the **real**
+  `WorldClockRepositoryImpl` across `FakeWorldClockDao` (so `addIfAbsent` and
+  `reorder`'s real transactions run) and a real DataStore under a `@TempDir`.
+  Three new `ArchitectureRulesTest` rules; the four new instrumentation tests
+  bring the compiled total to 40.
+
+  The decisions worth knowing: **there is no engine and must not be one** — a
+  world clock owns no AlarmManager slot, no service and no ring session, so a
+  fourth engine would be three empty seams and a `Mutex` guarding nothing; the
+  tab reads the **wall clock**, and re-reads both the instant and the device
+  zone on **every tick**, which is what makes `TIME_SET` and `TIMEZONE_CHANGED`
+  free (no new receiver branch); the zone **ids** stay pure (through a new
+  `ZoneProvider.available()`) while only the **names** cross the ICU seam, which
+  is one file, `runCatching`-guarded end to end and pinned there by a build
+  rule; the catalog keeps only region-based ids that are **their own canonical
+  id** — so the tzdata's own canonicalisation drops Asia/Calcutta in favour of
+  Asia/Kolkata and no table of ours can rot — unless the canonical id is not on
+  the device at all, since ICU and tzdata are separately updatable APEX modules
+  that can disagree, plus `UTC` by name; search is
+  **word-prefix over folded text**, so "erl" deliberately does not find Berlin;
+  the offset and day are computed **at the instant** from both zones' rules, the
+  same discipline `AlarmOccurrences` uses, so Berlin↔Sydney is ten hours in
+  January and eight in July; labels are **data, not strings**, so Kathmandu is
+  `Ahead(4, 45)` rather than a signed 285 for a translator to interpret; the
+  cadence is **200 ms** with the state truncated to the second (face) and the
+  minute (rows) and `distinctUntilChanged` over it; the list is capped at
+  **24**, with the cap spelled out on the screen once it is reached, because
+  M3's `ExtendedFloatingActionButton` has no `enabled` to dim; and
+  reduce-motion snaps the morph but **never stops the second hand**,
+  because a clock whose second hand stops is a broken clock.
+
+  Three things outside the checklist were changed anyway, and are recorded in
+  `ARCHITECTURE.md`: **`ZoneProvider` gained `available()`**, because
+  `ZoneId.getAvailableZoneIds()` at a call site is the same ambient read
+  `PLAN.md` §5 bans for `now()`; **`ui/common/AlarmTimeFormatter.kt` gained
+  `rememberLocalTimeFormatter`** with the existing function delegating to it, so
+  M5's "one 12/24-hour formatter" survives a fourth caller instead of growing a
+  second answer; and **`ShellDefaults.EmptyTabScreen` was deleted**, its own
+  KDoc having said it existed only until each of M5–M8 replaced its own tab —
+  the world clock was its last caller.
+
+  No schema change at all (the database stays at v2; `WorldClockEntity`, its
+  DAO, its mapper and its repository are not edited), **no new permission and no
+  manifest entry**, **one** new dependency coordinate —
+  `androidx.graphics:graphics-shapes:1.0.1`, pinned to the version that already
+  resolved transitively, because M8 imports that package directly — and **no
+  floret-kit change**: the kit stays at 0.6.0, untouched, with
+  `ReorderableColumn`, `GroupedSurface`, `FullScreenPicker`, `InlineTextField`
+  and `CollapsingScaffold`'s FAB slot already covering the screen.
+
+  Knowingly open: no rename UI for `world_clocks.label` — the column is honoured
+  on read and M10's backup import will carry labels; no automatic "home" row
+  while travelling (a separate feature with its own preference, and the hero
+  face already follows the device); no per-city detail screen, map,
+  sunrise/sunset or day-length bar — `DayNight` is a stated convention for a
+  shape morph, not an ephemeris; no live times or long zone names in the picker;
+  no seeded data, so a fresh install really has an empty list; no reordering by
+  anything but `sort_order`; and no `MaterialShapes` on the ring screen or timer
+  progress, which `PLAN.md` §8 also sanctions — the build rule makes widening
+  that allowlist a deliberate edit. The four new instrumentation tests compile
+  in the gate but have **never run on hardware**, as no device was attached —
+  the same caveat M5's seven, M6's four and M7's four carry.
+
 ### ⬜ M9 — System interop
 The full `android.provider.AlarmClock` contract (`PLAN.md` §6): `SET_ALARM`,
 `SET_TIMER`, `SHOW_ALARMS`, `SHOW_TIMERS`, `DISMISS_ALARM`, `SNOOZE_ALARM`, plus