fix(maestro): third-review findings — nested worktrees, staleness, placement

The one that loses data: the project picker lists linked worktrees as
pickable rows, so `base_repo` was easily a worktree rather than the main
checkout, and the new placement then nested the tree inside it. Git hides
a registered worktree's contents from the outer `git status`, so the
outer tree read clean and removing it deleted the inner one's uncommitted
work — while that session could still be running. Placement now resolves
to the main checkout via `--git-common-dir`, and removal refuses outright
when `worktree list` reports anything registered underneath.

Also:

- The `worktree_root` override dropped the old UUID without replacing it,
  so two repos spawning the same branch name targeted one directory and
  the second failed. The repo basename now sits between root and slug.
- Project staleness read `.git/HEAD`'s mtime, which only moves on
  checkout. A repo committed to daily from one long-lived branch reported
  its last branch switch and got dimmed. Prefer `logs/HEAD`.
- The projects cache TTL (5s) was shorter than its own background refresh
  (60s), so nearly every request rescanned all of $HOME under the scanner
  lock — and draft panes re-request on unrelated re-renders. Now 180s.
- onSuccess resolved the leaf against the active tab only, so switching
  tabs mid-POST orphaned the session. Searches every tab.

web/src/multiview.ts

@@ -154,13 +154,14 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
         onSuccess: (session) => {
           // The pane can be closed while the POST is in flight. Mounting the
           // session onto a leaf no longer in the tree would strand it in no
-          // pane at all, so only claim the leaf while it is still there.
-          const t = activeTab(layout);
-          const attached = leaves(t.root).includes(leaf);
-          if (attached) {
+          // pane at all, so only claim the leaf while it is still there —
+          // searching every tab, since the operator may have switched tabs
+          // while the request was in flight.
+          const host = layout.tabs.find((t) => leaves(t.root).includes(leaf));
+          if (host) {
             leaf.sessionId = session.id;
             leaf.draft = null;
-            t.focusedLeafId = leaf.id;
+            host.focusedLeafId = leaf.id;
           }
           render();
           opts.onOpenSessionsChange?.();