fix(continual-learning): harden wasRealCollision verifier (Codex review)

Addresses the P1 brittleness in the Step 3 verifier so learned_from edges
(graph/live.ts:413) can't be silently zeroed on stage.

- Capture overlap AT detection time as Collision.gitOverlap (podman.ts), while
  engineer_states are still fresh, instead of re-deriving from possibly-stale
  state when the user clicks. deriveWasRealCollision() now prefers this stored
  evidence and only falls back to a live re-derivation for older collisions.
- Canonicalize engineer names (trim + lowercase) on both the capture and the
  fallback path, so "Karti" vs "karti" no longer misses the git state.
- conflictKey now reuses the shared comparableBasename() helper (dedupe).

shared/src/collision.ts gains optional `gitOverlap?: boolean` (additive).
shared rebuilt; backend+frontend typecheck + eslint pass. PLAN.md rung 3 updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

shared/src/collision.ts

@@ -16,6 +16,14 @@ export interface Collision {
   severity: CollisionSeverity;
   /** Snapshot of relevant GitHub state at detection time. */
   githubState?: GithubStateSnapshot;
+  /**
+   * Git ground-truth overlap captured AT detection time, while engineer_states
+   * are still fresh: true when every involved engineer had `file` in their git
+   * changedFiles. Read as the authoritative wasRealCollision evidence at outcome
+   * time, so a late click, a stale sidecar, or the engineer_states freshness TTL
+   * cannot retroactively zero it out.
+   */
+  gitOverlap?: boolean;
   detectedAt: string;
 }