feat: session rename + graph chrome polish (popovers dismiss, no-shift no-match, coverage reseat)

Rename (owner ask): clicking the header title opens edit mode with the
whole title selected — typing replaces, arrows move inside. Enter or a
click away commits (PUT /api/chats/:id); Escape and an empty commit
discard. renameChat joins the ChatStore port; like saveSettings it is
NOT conversation activity — updatedAt stays put so sidebar order never
churns on a rename. The sidebar patch is instant: the header dispatches
lh:chat-renamed and SessionsSidebar folds it into its snapshot (the 2.5s
poll is only a backstop). Sidebar right-click rename is DELIBERATELY
deferred: it needs a real context-menu system, which gets its own pass
later (owner decision, 2026-09-17).

Graph chrome:
- The extraction-coverage button moves between search and import; the
  gear keeps the far-right corner. Coverage still renders on an EMPTY
  graph (that is exactly when it matters).
- The no-match search note no longer shifts its siblings: the chrome
  row is items-start (every button is 44px tall, so top alignment pins
  the row while the search container grows downward).
- Popovers dismiss properly: pointerdown anywhere outside the control's
  root (button + panel) closes it, and so does Escape. Two panels can
  never be open at once — the sibling chrome buttons are outside the open
  root, so pointerdown closes the first before the click opens the
  second. New shared hook components/popover-dismiss.ts, wired into
  both the settings gear and the coverage control.

Gates: typecheck, eslint, 498/498 (+2 rename store tests), build.
Live-verified: select-all/focus/Enter/Escape/empty/blur round-trip,
updatedAt untouched, sidebar instant patch; chrome order + frozen
positions under a no-match query; popover close via canvas, search
input, Esc, mutual exclusion, toggle intact.

components/sidebar.tsx

@@ -215,6 +215,18 @@ function SessionsSidebar() {
 		}
 	}, []);
 
+	/* Instant rename propagation (2026-09-17): the chat header's rename
+	   commits dispatch lh:chat-renamed; patch the snapshot in place instead
+	   of waiting for the 2.5s poll. */
+	useEffect(() => {
+		const onRenamed = (e: Event) => {
+			const { id, title } = (e as CustomEvent<{ id: string; title: string }>).detail;
+			setChats((prev) => (prev ? prev.map((c) => (c.id === id ? { ...c, title } : c)) : prev));
+		};
+		window.addEventListener("lh:chat-renamed", onRenamed);
+		return () => window.removeEventListener("lh:chat-renamed", onRenamed);
+	}, []);
+
 	useEffect(() => {
 		if (!open) return;
 		void refresh();