refactor(#3309): add health-diagnostic.cts skeleton (types + evaluator)

Phase 11 of epic #3180 (ADR-3180 §8.2/§8.3/§8.5). New src/health-diagnostic.cts:
SEVERITY/REMEDY_ACTION (7 members: 6 real repair actions + ADVISE)/REMEDY_RISK
(NONE/DESTRUCTIVE) frozen enums, Diagnostic/Remedy/Rule types, an empty RULES
table (rules land in the next commits), evaluateRules (with a duplicate-code
defense-in-depth check ahead of the lint guard), and applyRepairs (the
DESTRUCTIVE-risk-refusal dispatcher — §8.3 rule 3 — with stub handlers; real
repair bodies port in the migration step).

Six-gate .cts ripple: .gitignore, eslint.config.mjs, docs/INVENTORY.md +
manifest, CONTEXT.md glossary entry.

CONTEXT.md

@@ -106,6 +106,9 @@ Leaf module owning the frozen `SCOPE` discriminator (`COMPLETE` / `TRUNCATED` /
 ### Planning Snapshot Module
 Module owning the parsed projection of `.planning/` that a diagnostic rule may read, per ADR-3180 §8.1 (Decision 8, Phase 10, #3308). `buildPlanningSnapshot(cwd) → PlanningSnapshot` is composed EXCLUSIVELY from the already-consolidated §7 owners — `getMilestoneInfo` (Roadmap Parser Module), `listMilestonePhaseDirs` (Phase Locator Module), `isPhaseComplete` (Verification Module), `scanPhasePlans` (Plan Scan Module), `stateFieldValue`/`stateCurrentPositionSlice` (STATE.md Document Module), `planningPaths` (Planning Workspace Module) — and introduces no new semantic derivation of its own. `PlanningSnapshot` exposes `milestone`/`phaseDirs`/`phases`/`currentPhaseLabel`, each a `{value, scope}` pair per the Planning Scope Module's frozen `SCOPE` enum; `phases` additionally carries a `PhaseSnapshot[]` (`dir`, `complete`, `verificationStatus`, `planCount`, `summaryCount`, `scope`). The one new piece of logic this module adds is `worstScope(...scopes) → Scope`, a pure severity-ordered combinator (`UNREADABLE` > `UNSCOPED` > `TRUNCATED` > `COMPLETE`) that folds several independently-scoped owner answers about the same phase directory into one composite signal — NOT a re-derivation of any owner (each owner's own algorithm is untouched; only their already-computed `scope` verdicts are combined), but new coordination logic no single owner has the visibility to express. Every exposed field carries PARSED values only, never raw document text — this is structural, not advisory: a diagnostic rule given only the parsed value cannot re-derive a field's location the way `#3162`'s three inert `Current Phase` literal-search predicates did. Read failures on STATE.md (exists-but-unreadable, distinct from absent) are reported via the Unusable Input Diagnostic Module's `warnUnusableInput(UNUSABLE_REASON.STATE_UNREADABLE)`. Guarded by `scripts/lint-planning-snapshot-bypass-drift.cjs` (ratcheted per Decision 4(e), scoped to `DIAGNOSTIC_RULE_FUNCTIONS` — currently `cmdValidateHealth` in `src/verify.cts` only, acknowledging its existing raw `.planning/` reads as debt owned by Phase 11, #3309, which migrates it onto this snapshot). Source of truth: `gsd-core/bin/lib/planning-snapshot.cjs` (generated from `src/planning-snapshot.cts`). Design: `.gsd/phase/refactor-3308-planning-snapshot-parsed-projection/40-design.md`.
 
+### Health Diagnostic Module
+Module owning the frozen rule-table contract for `validate health`, per ADR-3180 §8.2/§8.3/§8.5 (Phase 11, #3309). Exposes three frozen enums — `SEVERITY` (`error`/`warning`/`info`), `REMEDY_ACTION` (the six real repair actions harvested from `cmdValidateHealth`'s existing `--repair` implementation — `createConfig`, `resetConfig`, `regenerateState`, `addNyquistKey`, `addAiIntegrationPhaseKey`, `backfillMilestones` — plus `advise`, the non-repairable payload every non-actionable finding's fix text becomes), and `REMEDY_RISK` (`none`/`destructive`) — plus the `Diagnostic`/`Remedy`/`Rule` shapes every rule's `check(snapshot: PlanningSnapshot) → Diagnostic[]` signature and every finding's `remedy` conform to. `RULES: Rule[]` is the rule table a later migration batch appends the 32 rules extracted from `cmdValidateHealth` (`src/verify.cts:1616-2577`) onto; this phase ships it EMPTY, establishing only the container and its type. `evaluateRules(snapshot) → Diagnostic[]` runs every rule in `RULES` against one `PlanningSnapshot` and flattens the results, throwing on any two rules sharing a `code` — defense in depth beside the future static 1:1 lint guard (§8.2 rule 1). `applyRepairs(cwd, diagnostics, repair, backfill) → {applied, refused}` is the `--repair`/`--backfill` dispatcher: a `DESTRUCTIVE` remedy (`resetConfig`/`regenerateState` — health.md's own published table: "loses custom settings" / "loses session history") is reported but never executed by `--repair`, a deliberate, disclosed breaking change (§8.3 rule 3) from `cmdValidateHealth`'s current unconditional application; `backfillMilestones` alone among the `NONE`-risk actions is requested by `--backfill` without `--repair`, mirroring `cmdValidateHealth`'s existing gate (`src/verify.cts:2504`). Per-action repair handlers are stubs in this phase — they land alongside the rules that need them. Source of truth: `gsd-core/bin/lib/health-diagnostic.cjs` (generated from `src/health-diagnostic.cts`). Design: `.gsd/phase/refactor-3309-health-diagnostic-rule-table/40-design.md`.
+
 ### Planning Workspace Module
 Module owning `.planning` path resolution, active workstream pointer policy (`session-scoped > shared`), pointer self-heal behavior, and planning lock semantics for workstream-aware execution.