fix(project-name): use parent/worktree composite so observations don't cross worktrees

Revert of #1820 behavior. Each worktree now gets its own bucket:
- In a worktree, primary = `parent/worktree` (e.g. `claude-mem/dar-es-salaam`)
- In a main repo, primary = basename (unchanged)
- allProjects is always `[primary]` — strict isolation at query time

Includes a one-off maintenance script (scripts/worktree-remap.ts) that
retroactively reattributes past sessions to their worktree using path
signals in observations and user prompts. Two-rule inference keeps the
remap high-confidence:
  1. The worktree basename in the path matches the session's current
     plain project name (pre-#1820 era; trusted).
  2. Or all worktree path signals converge on a single (parent, worktree)
     across the session.
Ambiguous sessions are skipped.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/utils/project-name.test.ts

@@ -97,7 +97,7 @@ describe('getProjectContext', () => {
     expect(ctx.parent).toBeNull();
   });
 
-  describe('worktree regression (#1081, #1500, #1819)', () => {
+  describe('worktree isolation', () => {
     let tmp: string;
     let mainRepo: string;
     let worktreeCheckout: string;
@@ -125,21 +125,18 @@ describe('getProjectContext', () => {
       rmSync(tmp, { recursive: true, force: true });
     });
 
-    it('uses parent project name as primary when in a worktree', () => {
+    it('uses parent/worktree composite as primary when in a worktree', () => {
       const ctx = getProjectContext(worktreeCheckout);
       expect(ctx.isWorktree).toBe(true);
-      expect(ctx.primary).toBe('main-repo');
+      expect(ctx.primary).toBe('main-repo/my-worktree');
       expect(ctx.parent).toBe('main-repo');
-      expect(ctx.allProjects).toEqual(['main-repo', 'my-worktree']);
+      expect(ctx.allProjects).toEqual(['main-repo/my-worktree']);
     });
 
-    it('write-path call sites resolve to parent project in worktrees', () => {
-      // Mirrors the pattern used by session-init.ts and SessionRoutes.ts:
-      //   const project = getProjectContext(cwd).primary;
-      // This must resolve to the parent repo, not the worktree name,
-      // so observations are stored under the correct project.
+    it('write-path call sites resolve to composite name in worktrees', () => {
       const project = getProjectContext(worktreeCheckout).primary;
-      expect(project).toBe('main-repo');
+      expect(project).toBe('main-repo/my-worktree');
+      expect(project).not.toBe('main-repo');
       expect(project).not.toBe('my-worktree');
     });
   });