docs: changelog, docs/ set, CONTRIBUTING, LICENSE

Bring floret-kit up to the family's repo conventions:
- CHANGELOG.md (Keep a Changelog) — what each module added.
- README.md — full module table (core-time/core-crash/identity/components) +
  consumption notes and a docs index.
- docs/README.md (index), docs/ARCHITECTURE.md (module layering, the submodule +
  composite-build consumption model, JVM vs android-library, the reproducibility
  rules, the share-mechanics-not-look contract), docs/ROADMAP.md (extracted vs
  deferred vs deliberately-not-shared, from the cross-app survey).
- CONTRIBUTING.md — the no-app-coupling rules, how to add a module, how an app
  adopts the kit.
- LICENSE (MIT, matching the apps).

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

CONTRIBUTING.md

@@ -0,0 +1,77 @@
+# Contributing to floret-kit
+
+floret-kit is the shared Material 3 Expressive design system + plumbing for the
+Floret app family. Before changing it, skim
+[`docs/ARCHITECTURE.md`](docs/ARCHITECTURE.md) (how it's built and consumed) and
+[`docs/ROADMAP.md`](docs/ROADMAP.md) (what's in scope). This file is the
+practical how.
+
+## The rules
+
+1. **Share mechanics, not look.** Extract the machinery; leave seed colours,
+   palettes, identity chips, and wording to the apps. If a piece can't be made
+   app-agnostic without contortion, it doesn't belong here yet.
+2. **No app coupling.** A kit module never imports an app package, an app's `R`,
+   or a domain type. App-specific values arrive as **constructor/config
+   parameters** or **callbacks** (see `core-crash`'s `CrashConfig`,
+   `InlineTextField`'s `capitalization`).
+3. **String resources are fallbacks.** Kit strings are English defaults an app
+   overrides via resource merge. Don't put app-specific or per-app-divergent
+   wording in the kit.
+4. **Bake divergence into parameters, don't pick a silent winner.** Where two
+   apps differ, expose the difference. When a shared primitive adopts one app's
+   version as canonical, that's a deliberate, documented convergence.
+5. **No `foojay` toolchain resolver** — not in any `*.gradle.kts`, not even as a
+   token in a comment. It breaks reproducible / official F-Droid builds. Set
+   `jvmTarget` directly. See [`docs/ARCHITECTURE.md`](docs/ARCHITECTURE.md) §5.
+
+## Prerequisites
+
+- JDK 17
+- Android SDK (compileSdk 37) for the Android modules — set `ANDROID_HOME` or add
+  a gitignored `local.properties` with `sdk.dir`. Pure-JVM modules need neither.
+
+## Build & test
+
+```sh
+./gradlew :core-time:test              # JVM module (JUnit 5 + Truth)
+./gradlew :core-crash:testDebugUnitTest
+./gradlew :identity:assembleDebug
+./gradlew build                        # everything
+```
+
+In practice the kit is exercised through a consuming app's composite build (e.g.
+`agendula`'s `./gradlew assembleDebug`), which compiles the included modules from
+source.
+
+## Adding a module
+
+1. Create `:<module>` and add `include(":<module>")` to
+   [`settings.gradle.kts`](settings.gradle.kts).
+2. Add a `<module>/build.gradle.kts`:
+   - **JVM:** `plugins { alias(libs.plugins.kotlin.jvm) }`, a `kotlin { compilerOptions { jvmTarget = JVM_17 } }` block, JUnit 5 test deps.
+   - **Android:** `plugins { alias(libs.plugins.android.library); alias(libs.plugins.kotlin.compose) }` (no `kotlin.android` — AGP 9.x is built-in), `namespace = "de.jeanlucmakiola.floret.<area>"`, `compileSdk 37` / `minSdk 29`, `jvmTarget = JVM_17`.
+3. Put sources under `src/main/kotlin/de/jeanlucmakiola/floret/<area>/`. The root
+   build's `subprojects {}` sets the shared `group`/`version`, so no per-module
+   coordinates are needed.
+4. Add an entry to [`CHANGELOG.md`](CHANGELOG.md), the README module table, and
+   (if status-worthy) [`docs/ROADMAP.md`](docs/ROADMAP.md).
+
+## Adopting the kit in an app
+
+1. `git submodule add <kit-url> floret-kit`.
+2. `includeBuild("floret-kit")` in the app's `settings.gradle.kts`.
+3. `implementation("de.jeanlucmakiola.floret:<module>")` in the app module.
+4. Ensure CI checks out submodules (`submodules: recursive`) and the included
+   build can find the SDK (`ANDROID_HOME`). For official F-Droid reproducible
+   builds, add `submodules: true` to the fdroiddata recipe and have the repro
+   guard scan the submodule.
+5. The app pins a kit commit via the submodule; bump it deliberately to adopt kit
+   changes.
+
+## Validate before pushing
+
+- `python3 -c "import yaml; yaml.safe_load(open('<workflow>.yml'))"` after any
+  workflow edit — indentation bites.
+- A consuming app's `lintDebug` + `testDebugUnitTest` + `assembleDebug` should be
+  green after a kit change you mean to land.