[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/tracker_entry.schema.json

@@ -12,6 +12,19 @@
     "date": { "$ref": "enums.schema.json#/$defs/DateString" },
     "value": { "$ref": "enums.schema.json#/$defs/TrackerValue" },
     "logged_at": { "$ref": "enums.schema.json#/$defs/DateTimeString" },
-    "note": { "type": "string", "maxLength": 200, "description": "선택. 길게 쓰지 말 것" }
+    "note": { "type": "string", "maxLength": 200, "description": "선택. 길게 쓰지 말 것" },
+    "variant_id": {
+      "type": "string",
+      "description": "선택된 habit.dose_variants[].id. value=done일 때만 의미 있음. value=blank면 무시."
+    },
+    "context_snapshot": {
+      "type": "object",
+      "additionalProperties": false,
+      "description": "체크인 시점 컨텍스트 (variant 추천에 쓰인 입력). 회고·집계용 스냅샷.",
+      "properties": {
+        "location": { "type": "string", "description": "예: '짐', '집', '출장'" },
+        "condition": { "type": "string", "description": "예: '좋음', '보통', '나쁨'" }
+      }
+    }
   }
 }