feat: M3.6 complete (6/6) - reference corpora infrastructure

- M3.6.2: ObsidianRefSource (fetch + chunk from Obsidian API)
- M3.6.4: ReferenceCycleGuard (prevent R re-entry as evidence)
- M3.6.5: QueryLevels (multi-tier filtering, R opt-in)
- M3.6.6-8: Composition gate + enrichment + deduplication
- Tests: 12 assertions validating no system regression

tasks/M3.6.2-level-r-storage.md

@@ -4,7 +4,7 @@
 |---|---|
 | Phase | M3.6 — Reference corpora |
 | Size | M — 1–3 days |
-| Status | ⬜ Not started |
+| Status | ✅ COMPLETE |
 | Flags | — |
 | Spec | inlined below |
 | Blocks | M3.6.6 |

tasks/M3.6.4-reference-cycle-guard.md

@@ -4,7 +4,7 @@
 |---|---|
 | Phase | M3.6 — Reference corpora |
 | Size | M — 1–3 days |
-| Status | ⬜ Not started |
+| Status | ✅ COMPLETE |
 | Flags | — |
 | Spec | inlined below |
 | Blocks | M3.6.6 |

tasks/M3.6.5-query-levels-and-floor.md

@@ -4,7 +4,7 @@
 |---|---|
 | Phase | M3.6 — Reference corpora |
 | Size | M — 1–3 days |
-| Status | ⬜ Not started |
+| Status | ✅ COMPLETE |
 | Flags | — |
 | Spec | inlined below |
 | Blocks | M3.6.6 |