Track web pane URLs in bridge for layout capture

[kordless]

Goal

Extend the bridge's TrackedSession type to include webUrl so that layout save (#82) can capture web pane URLs without an extra IPC roundtrip.

Current state

• app/bridge.ts:34-51 TrackedSession tracks: rows, cols, name, tabName, description, rootTabUid, windowId, splitLabel, tabOrder, tabActive, paneActive, bspX/Y/W/H
• Web pane URL lives in renderer Redux at termGroups[uid].webUrl (typings/hyper.d.ts:33)
• No flow from renderer to bridge for URL changes

Scope

• Add webUrl?: string | null to TrackedSession interface
• Add an exported function updateSessionWebUrl(uid, url) in bridge.ts
• In renderer, when a webUrl reducer action fires (lib/reducers/term-groups.ts:234, 242), fire an RPC to main → call updateSessionWebUrl
• Add an IPC 'session web url' handler in app/ui/window.ts that calls updateSessionWebUrl

Why this matters

• Without bridge tracking, layout save needs an IPC roundtrip on every close to fetch URLs from Redux
• With bridge tracking, the main process can iterate trackedSessions filtered by windowId and emit URLs directly

Files touched

• app/bridge.ts — extend TrackedSession, add updateSessionWebUrl
• app/ui/window.ts — register RPC handler
• lib/reducers/term-groups.ts — emit RPC alongside reducer dispatch (or via a thunk)

Depends on

None — can ship independently. Unblocks #82 from needing per-pane IPC fetches.