[Architect] Refs #204 — adopt dose_variants design (ADR-0001)

Resolves the long-pending dose variant decision before Phase 1 schema work:
- habit.dose_variants[] added (id/label/dose_text/context_tags/condition_tags/is_minimum), no cardinality cap.
- tracker_entry gains variant_id + context_snapshot{location,condition}.
- reflection gains weekly minimum_ratio (hint-only).
- data-model.md: R9 (≤4) retired; new R9 (no cap, UX-side enforcement) + R10 (weekly minimum_ratio hint, no threshold).
- docs/adr/0001-dose-variants.md captures rationale + alternatives.

Why now: Phase 1 (#204) needs the final schema shape before Drift DDL is drawn.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

schema/reflection.schema.json

@@ -17,6 +17,12 @@
     "missed": { "type": "string", "description": "결석/lapse 패턴 — 자책 아닌 데이터 처리" },
     "adjust": { "type": "string", "description": "다음 주기에 바꿀 것 1개만" },
     "identity_note": { "type": "string", "description": "L3 정체성 변화 감각 (옵션)" },
+    "minimum_ratio": {
+      "type": "number",
+      "minimum": 0,
+      "maximum": 1,
+      "description": "scope=weekly에 한해 집계. 해당 기간 done 체크인 중 is_minimum=true variant 비율. application layer 계산. UI: 'tiny가 자주 고정' 감지 hint 용 (강제 X)."
+    },
     "created_at": { "$ref": "enums.schema.json#/$defs/DateTimeString" }
   }
 }