docs(joinir): Phase 80 Tasks 80-0/80-A - Status verification + design doc

Task 80-0: Current status verification
- ✅ 970/970 lib tests PASS (production stable)
- ✅ Core VM smoke tests PASS (json_pp_vm)
- ❌ Phase 79 E2E tests broken (AST API mismatch, out-of-scope)
- ❌ Pre-existing json_lint_vm failure (Pattern2 verifier, out-of-scope)
- **Conclusion**: Phase 80 has ZERO blockers

Task 80-A: SSOT design doc created
- New: docs/development/current/main/phase80-bindingid-p3p4-plan.md (336 lines)
- Pattern3/4 BindingId wiring strategy
- Implementation order: 80-B (P3) → 80-C (P4) → 80-D (E2E)
- Code examples and success metrics
- Fallback detection mechanism (existing log tags)

Design principles (consistent with Phase 74-79):
- Dev-only code (feature-gated)
- Dual-path maintained (BindingId priority + name fallback)
- Structural detection only (NO by-name branching)
- Fail-Fast error handling
- Zero production impact

Updated docs:
- 01-JoinIR-Selfhost-INDEX.md: Phase 79 Activation status
- 10-Now.md: Phase 80 tasks 80-0/80-A complete
- 20-Decisions.md: BindingId migration complete status
- joinir-architecture-overview.md: Phase 79/80 sections

Next: Task 80-B (Pattern3 BindingId registration)

docs/development/current/main/joinir-architecture-overview.md

@@ -131,6 +131,10 @@ JoinIR ラインで守るべきルールを先に書いておくよ：
     - 次の焦点（Phase 73+）:
       - JoinIR lowering の `ScopeManager` を「名前ベース」から「BindingId ベース」に段階移行し、shadowing/束縛同一性を JoinIR 側でも安全に扱えるようにする。
       - 参照: `docs/development/current/main/phase73-scope-manager-design.md`
+      - promoted carriers（DigitPos/Trim）の “synthetic name” 問題を BindingId で接続する（dev-only）:
+        - 参照: `docs/development/current/main/phase78-bindingid-promoted-carriers.md`
+      - 次の配線計画（P3/P4 拡張）:
+        - 参照: `docs/development/current/main/phase80-bindingid-p3p4-plan.md`
 
 13. **Ownership/Relay（Phase 56–71）: carrier/capture/relay を契約化する（dev-only）**
     - `OwnershipPlan` は carriers/captures/relay_writes の SSOT として使い、混線を Fail-Fast で検出する。