feat: per-stage traceability enforcement with deterministic JSON sensor

[jeromevdl]

Summary

Adds element-level traceability enforcement across the AIDLC workflow — ensuring nothing from the initial intent (requirements, stories, acceptance criteria) is silently dropped between stages.

What this adds

Stable ID conventions (enforced in stage prose)

• FR{n}, NFR{n} — requirements-analysis
• US{n}.{m} — user-stories
• AC{story}.{seq} (3-segment) — user-stories
• BR{group}.{seq} — functional-design
• NFRx.y — nfr-requirements decomposition
• U{n} / u{n}-{desc} — units-generation naming

Per-stage traceability.json

Each stage produces a structured JSON file mapping upstream elements to downstream coverage:

{
  "stage": "functional-design",
  "unit": "u1-auth",
  "upstream_ids": ["AC1.1.1", "AC1.1.2"],
  "coverage": [
    { "id": "AC1.1.1", "status": "OK", "target": "BR01" },
    { "id": "AC1.1.2", "status": "GAP" }
  ],
  "reverse": [
    { "id": "BR03", "status": "ORPHAN" }
  ]
}

Deterministic traceability sensor

aidlc-sensor-traceability.ts fires at each gate with three checks:

1. Minimum coverage — empty file fails
2. Status scan — GAP/ORPHAN entries are findings; Deferred/N/A without target are findings
3. Upstream ID cross-check — extracts IDs from upstream files via regex, compares against declared upstream_ids. Two independent sources must agree.

Per-unit stages scope via unit-of-work-story-map.md to avoid false positives across units.

Phase boundaries

• delivery-planning (Inception exit): aggregates upstream traceability files, checks for gaps
• build-and-test (Construction exit): final coverage gate — verifies all FRs/ACs/NFRs from inception have implementing code across all units

Other changes

• Moved Construction→Operation boundary from ci-pipeline (conditional) to build-and-test (always runs)
• Fixed typo in infrastructure-design.md
• Regenerated stale t66 designer-export fixture (agents 11→13, pre-existing)
• Updated docs and knowledge base

Known limitations

• Ideation→Inception boundary untouched — no numbered IDs at that phase (exploratory by design)
• Unit-name join assumes u{n} convention — advisory warning emitted on naming mismatch
• Free-text elements (component names) not diffable — marker scan only for units-generation
• build-and-test final gate is prose-instructed — not sensor-enforced (cross-unit aggregation)

Pre-existing test failures (not introduced by this PR)

• t65 round-trip: YAML emitter issue on v2 branch
• t68 version badge: v2 branch version mismatch (0.7.12 vs 2.0.0 in README)