fix(worktree): audit observation fetch/display for composite project names

Three sites didn't account for parent/worktree composite naming:

- PaginationHelper.stripProjectPath: marker used full composite, breaking
  path sanitization for worktrees checked out outside a parent/leaf layout.
  Now extracts the leaf segment.
- observations/store.ts: fallback imported getCurrentProjectName from
  shared/paths.ts (a duplicate impl without worktree detection). Switched
  to getProjectContext().primary so writes key into the same project as
  reads.
- SearchManager.getRecentContext: fallback used basename(cwd) and lost
  the parent prefix, making the MCP tool find nothing in worktrees.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/services/worker/PaginationHelper.ts

@@ -24,15 +24,17 @@ export class PaginationHelper {
    * Uses first occurrence of project name from left (project root)
    */
   private stripProjectPath(filePath: string, projectName: string): string {
-    const marker = `/${projectName}/`;
+    // Composite names ("parent/worktree") don't appear in on-disk paths for
+    // standard git worktrees — only the checkout basename does. Match on the
+    // leaf segment so the heuristic works regardless of worktree layout.
+    const leaf = projectName.includes('/') ? projectName.split('/').pop()! : projectName;
+    const marker = `/${leaf}/`;
     const index = filePath.indexOf(marker);
 
     if (index !== -1) {
-      // Strip everything before and including the project name
       return filePath.substring(index + marker.length);
     }
 
-    // Fallback: return original path if project name not found
     return filePath;
   }