[Release] #215 v0.2.0 — Phase 2-A on-device Gemma frame suggestion

Bump app version 0.1.0+1 → 0.2.0+2 (minor — new feature surface).
CHANGELOG.md 신설 — v0.2.0 (#215 Phase 2-A) + v0.1.0 (#204 Phase 1) 회고 기록.

릴리스 산출물:
- APK release 58.4MB (debug 키 서명 — production 키는 future issue)
- 71 tests pass / analyze 0 issues
- 9/10 AC PASS, AC10 (한국어 corpus) DEFER → OQ-1 후속

알려진 제약:
- _kModelUrlPlaceholder 상태 (OQ-1 미해결)
- F1: 60s idle auto-unload 미구현 (stub 라 무의미)
- F2: purge() File.delete try/catch 미감쌈 (도달 불가)

Refs #215

app/pubspec.yaml

@@ -1,7 +1,7 @@
 name: life_helper
 description: "Huberman + Atomic Habits + Tiny Habits + If-Then. Local-first habit/checklist/todo."
 publish_to: 'none'
-version: 0.1.0+1
+version: 0.2.0+2
 
 environment:
   sdk: ^3.12.2