docs: add architecture, roadmap, releasing, contributing + docs index

Add a grounded doc set under docs/ plus a root CONTRIBUTING.md:
- docs/ARCHITECTURE.md: current code shape (layers, data seam, provider
  resolution, reminder engine, DI, build/tooling, manifest)
- docs/ROADMAP.md: status view (M0/M1 done, M2 in progress, open decisions)
- docs/RELEASING.md: tag-driven release flow, CI jobs, F-Droid repo, secrets
  (was referenced by build.gradle.kts and CHANGELOG but missing)
- docs/README.md: docs index and how the docs relate
- CONTRIBUTING.md: build/test/lint, layer rules, style, PR conventions

Also refresh the stale "M0 — skeleton" status note in README.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/ROADMAP.md

@@ -0,0 +1,105 @@
+# Floret — roadmap
+
+Where the project is and where it's going. This is the **status** view; the
+design rationale behind each milestone lives in [`PLAN.md`](PLAN.md), and how the
+pieces fit together is in [`ARCHITECTURE.md`](ARCHITECTURE.md).
+
+Status legend: ✅ done · 🚧 in progress · ⬜ not started
+
+---
+
+## Current state (one line)
+
+The full non-visual stack ("backoffice") over the OpenTasks `TaskContract`
+provider is **done and unit-tested**; the Material 3 Expressive UI is being
+built screen by screen on top of it. App builds, gates on provider/permission,
+and renders the lists overview.
+
+---
+
+## Milestones
+
+### ✅ M0 — Skeleton
+Project scaffolding copied from Calendula (Gradle, version catalog, Hilt,
+Material 3 Expressive theme, Gitea CI/release workflows, F-Droid metadata),
+reseeded to a warm-mauve fallback palette. Builds, shows a themed placeholder.
+
+### ✅ M1 — Read path + logic (the "backoffice")
+The complete non-visual stack:
+- Vendored `TaskContract` subset, `ProviderResolver` (runtime authority
+  detection), `ColumnReader`, mappers, `AndroidTasksDataSource` (Instances
+  query + `ContentObserver`), and `TasksRepository` exposing live Flows of
+  lists / tasks / detail.
+- Domain models, smart-list filtering (Today / Upcoming / Overdue / No-date /
+  All / Completed), sorting, form validation, subtasks via `parentId`.
+- Self-scheduled due-reminder engine (AlarmManager + boot / provider-change
+  re-sync), notifications, DataStore prefs.
+- Render-only ViewModels + UiState for **every** screen, so the UI is build-only
+  from here.
+- JVM unit tests across mappers, filtering, sorting, form, value mapping, and
+  day windows.
+
+### 🚧 M2 — Screens: lists, task list, complete & CRUD
+Replace the functional scaffold with the real Material 3 Expressive UI, screen
+by screen, against the already-built ViewModels.
+- ✅ Provider/permission onboarding gate (`RootScreen`).
+- ✅ Lists overview (`ListsScreen`) — smart lists + user lists grouped by account.
+- 🚧 Navigation host wiring (the `onOpenFilter` / `onNewTask` callbacks in
+  `RootScreen` are currently stubs).
+- ⬜ Task list screen — checkbox rows, swipe-to-complete / swipe-to-delete,
+  inline add field, section headers for smart lists, FAB.
+- ⬜ Toggle complete (swipe + checkbox), create / edit / delete, local-list
+  creation wired to the UI.
+
+### ⬜ M3 — Detail / edit polish
+Task detail and edit screens: due/start date-time pickers, priority,
+percent-complete, conflict-safe saves (re-check before overwrite), smart-list
+section presentation.
+
+### ⬜ M4 — Subtasks (UI)
+`RELATED-TO` hierarchy in the UI: indentation, create subtask, reparent. The
+data layer already reads `parentId`; this is the trickiest UI piece.
+
+### ⬜ M5 — Reminders onboarding & polish
+The engine exists (M1). Remaining: the `POST_NOTIFICATIONS` + exact-alarm
+onboarding flow, per-task / default reminder-offset settings UI, and
+end-to-end verification on device.
+
+### ⬜ M6 — Settings, widget, i18n, release
+Settings screen (theme / dynamic-color / language, default list, default
+reminder), Glance task-list widget, translations, finalize F-Droid metadata,
+confirm CI release flow.
+
+### ⬜ Posture B (separate track, later)
+Add a `:provider` module bundling the Apache-2.0 `opentasks-provider`;
+`ProviderResolver` defaults to our own `org.dmfs.tasks`; add sync-adapter
+permissions; ship self-contained. UI / repository / domain untouched — see
+[`ARCHITECTURE.md`](ARCHITECTURE.md) §7.
+
+---
+
+## Open decisions / to verify
+
+These carry over from [`PLAN.md`](PLAN.md) §9; resolved ones are struck through.
+
+1. ~~**Name** — `Floret`~~ confirmed (appId `de.jeanlucmakiola.floret`).
+2. ~~**tasks.org provider authority**~~ verified on device:
+   `org.tasks.opentasks` + `org.tasks.permission.*`.
+3. **jtx Board** — support its richer contract later, or stay OpenTasks-only?
+   (Not in the candidate list today.)
+4. **Posture B authority choice** — bundling `org.dmfs.tasks` makes Floret a
+   *replacement* for OpenTasks (one authority owner per device). Intended, but a
+   conscious choice.
+5. **Recurring tasks** — read as occurrences today (`isRecurring` flag exists);
+   recurrence-aware editing is out of scope for v1.
+
+---
+
+## How to contribute / verify
+
+- Build: `./gradlew :app:assembleDebug`
+- Unit tests: `./gradlew :app:testDebugUnitTest`
+- Run on a device/emulator that has **OpenTasks** or **tasks.org** installed (and
+  ideally DAVx5 syncing a CalDAV task list) so the read/write paths have real
+  data. Debug builds use `DemoSeeder` for sample data when no provider data is
+  present.