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>

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Jean-Luc Makiola
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.