refactor: Reorganize docs folder structure for clarity and version management (PR 3c)

Reorganize documentation following AGENTS.md v16.0 governance (traceability, reproducibility):

Structure changes:
- CURRENT/ (new)
  ├─ 00~08.md (v16.0 standards, renamed for clarity)
  └─ CATALOGS/ (9 CSV files: WBS, decision log, debt register, matrices, catalogs)

- LEGACY/ (new, read-only archives)
  ├─ v11/ (original baseline + hardening analysis)
  ├─ v12~v15/ (.gitkeep + README for future archiving)

- DECISIONS/ (new, ready for ADR usage)
- TEMPLATES/ (existing, unchanged)

Deletions (consolidated into CURRENT/):
- v16_0/ folder (files migrated)
- hardening/ folder (contents → LEGACY/v11/)
- Root-level v11 files (00~07.md, CSV)

Renames (for clarity):
- 00_EXECUTIVE_REFERENCE_IMPLEMENTATION.md → 00_EXECUTIVE.md
- 01_BRUTAL_ROLE_AUDIT.md → 01_ROLE_AUDIT.md
- 02_FRONTEND_ADAPTER_CRUD_STANDARD.md → 02_FE_ADAPTER.md
- 03_BACKEND_DATA_SCHEDULER_STANDARD.md → 03_BE_DATA.md
- 04_ALGORITHM_MODEL_GOVERNANCE.md → 04_ALGORITHM.md
- 05_PROCESS_VIBE_DEBT_CONTROL.md → 05_PROCESS_VIBE_DEBT.md
- 06_VALIDATION_TRUTH.md → 06_VALIDATION.md
- 07_PACKAGE_ATTACHMENT_POLICY.md → 07_PACKAGE_POLICY.md

Updates:
- docs/INDEX.md (complete rewrite with navigation)
- LEGACY/ folders with README + .gitkeep

Benefits:
✅ Clear version management (v16.0 is active, v11~v15 read-only)
✅ No version mixing in root
✅ CURRENT/ as single point of reference for active docs
✅ CATALOGS/ consolidates all data matrices
✅ LEGACY/ preserves history without clutter
✅ Traceability: decision log, tech debt, WBS all linked
✅ DECISIONS/ ready for ADR pattern (future use)

Sync with root:
- CLAUDE.md references: docs/CURRENT/, docs/INDEX.md ✅
- AGENTS.md references: docs/CURRENT/, traceability ✅
- README.md: Document guide links updated ✅

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

docs/LEGACY/v11/02_ALGORITHM_CONTRACT.md

@@ -0,0 +1,36 @@
+# Sell/Reentry Algorithm Contract
+
+## Decision Context
+
+- PortfolioId, AccountId, LotId, CycleId
+- AssetPolicyId, IPSVersion
+- AsOf, PublishedAtCutoff, TradableSession
+- EvidenceId, DatasetId, ModelVersion, ConfigVersion, CodeSha
+- CurrentLotQuantity, CurrentPortfolioWeight, StrategicCoreFloorWeight
+- Peak/Floor/Breach/Cooldown
+- Hard impairment evidence grade and approval
+- Risk reduction requirement, concentration excess, liquidity capacity
+- Expected utility component distribution and confidence lower bound
+
+## Decision Output
+
+- Action: HOLD/PARTIAL_SELL/FULL_SELL
+- PolicyId/Priority/ReasonCode
+- SellRatioOfLot
+- ProposedQuantity
+- TargetPortfolioWeightAfter
+- ReentryEligibility
+- CounterEvidence
+- ValidUntil/NextReviewSession
+- DecisionHash
+
+## Invariants
+
+1. Hard impairment cannot be overridden.
+2. Proposed quantity cannot exceed lot quantity.
+3. Strategic core floor cannot be breached unless an approved higher-priority policy allows it.
+4. Same input and Version Set produce the same decision hash.
+5. A decision without immutable Evidence cannot be stored.
+6. A reentry stage executes at most once.
+7. Reentry creates a new CycleId.
+8. Hard impairment cannot create an automatic ReentryWatch.