fix(maestro): group worktree sessions under their repository

The sidebar nested a worktree session under the worktree, so a repo grew
a <repo>/worktrees/<branch> folder holding one session of the same name,
and the repo stopped being where you look for the work.

The daemon recorded whatever base_repo the request named, which is the
worktree itself when spawning from inside one; it now records the
resolved main checkout. The web tree groups by that instead of the cwd.
The TUI sidebar is a flat list with no directory grouping, so it needs
no mirror.

Closes #99

web/src/tree.ts

@@ -2,7 +2,7 @@
 // so it can be tested directly.
 
 import type { Session } from "./types.js";
-import { abbreviateCwd, sessionCwd, sessionName } from "./types.js";
+import { abbreviateCwd, sessionName, sessionTreePath } from "./types.js";
 
 export interface TreeFolder {
   kind: "folder";
@@ -30,7 +30,9 @@ export function buildTree(sessions: Session[], home: string | undefined, filter:
   const lc = filter.trim().toLowerCase();
 
   for (const s of sessions) {
-    const cwd = sessionCwd(s);
+    // Grouped by repository, so a worktree session lands under its repo
+    // rather than in a folder of its own (#99).
+    const cwd = sessionTreePath(s);
     const dir = cwd ? abbreviateCwd(cwd, home) : "";
     if (lc) {
       const haystack = `${sessionName(s)} ${dir}`.toLowerCase();