feat(retry): per-gate retry budgets + progress-aware charging + hybrid salvage

Replaces the single shared per-stage retryCount (reset on TransitionExecuted,
shared across all post-stage gates) with a per-gate budget. Motivated by run
2e468f9f, where a promising freestyle run was terminally FAILED because the
contract gate burned all 3 shared retries on one trivial miss before the
semantic-review gate ever ran.

- StageExecutionResult.Failure gains a `gate` id; each gate tags its failures.
- OrchestrationState gains gateRetryBudgets / gateFailureFingerprints /
  gateSalvageUsed (all rebuilt from events, reset per-stage on TransitionExecuted).
- FailureFingerprint normalizes+hashes the failure reason; RetryCoordinator.decide
  charges a gate's budget only when the fingerprint is unchanged (no progress),
  so a moving run is never penalised. Returns Retry | Exhausted.
- Hybrid exhaustion: deterministic gates fail; the review gate consults a
  SalvageJudge (LLM, or a deterministic allow-one-reset fallback), recorded as
  RetrySalvageDecidedEvent (invariant #9). CONTINUE resets the gate budget once;
  a second exhaustion is terminal.
- Review gate is now the sole authority on review-retry termination; the old
  REVIEW_BLOCK_RETRY_CAP is repurposed as a high absolute backstop only.
- ServerModule escaped-exception path now records a truthful terminal
  WorkflowFailed (real stage/reason/retryExhausted) via recordUnhandledFailure.

Tests: DefaultRetryCoordinatorTest (fingerprint charging) +
GateRetryBudgetExhaustionTest (deterministic exhaust / review CONTINUE-then-
terminal / review FAIL / null-judge fallback) + reducer coverage.

core/transitions/src/main/kotlin/com/correx/core/transitions/execution/StageExecutionResult.kt

@@ -8,5 +8,9 @@ sealed interface StageExecutionResult {
     data class Failure(
         val reason: String,
         val retryable: Boolean,
+        // Budget key for per-gate retry accounting (see RetryCoordinator.decide). Default keeps
+        // back-compat for call sites that don't set a stable gate id (e.g. the main producer path) —
+        // those are budgeted under the single legacy "stage" bucket.
+        val gate: String = "stage",
     ) : StageExecutionResult
 }