Workspace Sidebar: tmux, worktree and manager sections (#331, #333)

[raiseCatError]

#331 and the navigation part of #333. Stacked on the workspace foundation PR (feature/workspace-foundation). Standalone controller and renderer; TerminalApp.ts untouched.

• SidebarController: selection by id across refreshes (a vanished one moves to the row in its place), expansion kept across refreshes, ← to the parent, a / filter showing matches with their ancestors. Moving only proposes a preview; activation returns an intent and only for an activatable resource; anything else returns its reason.
• renderSidebar: exactly rows × width; focus, selection, active, attention, exited and stale each have their own mark in Unicode and Safe glyphs, so NO_COLOR loses nothing; compact mode for narrow docks; key help only while focused.
• tmux.ts: one bounded list-panes -a on the server NMSh runs inside ($TMUX) — trusted executable, 1.5 s / 256 KiB, minimal environment, argv only. U+001F field separator (tmux rejects control characters in names, verified on tmux 3.7) and every row validated. Session → window → pane (two windows / five panes = one session); NMSh's own pane ($TMUX_PANE) marked active. Navigation uses tmux's own select-pane / select-window / switch-client on ids, never names. No panes, PTYs or layout changes.
• sources.ts: worktrees from the /worktrees snapshot (open = that manager's cd intent; missing/bare listed with a reason) and links to /github, /agents, /sessions.

Not included: NMSh live sessions and Managed Targets as first-class rows (need the session service and #329 registry wired through the frontend); GitHub items (the manager is linked).

Tests: tests/workspaceSidebar.test.ts, including a real tmux server on a private socket (listing, selecting a window with the navigation argv, a missing server reported as an error); skipped only when tmux is not installed.

Update (272f302): Ubuntu CI (tmux 3.4) listed no panes: that tmux escapes control characters in format output, so the U+001F separator never arrived. The listing now uses | with names requested through tmux's q: modifier; both escapings are undone and rows with the wrong field count are dropped. The design notes moved to docs/design/workspace-sidebar.md so the workspace slices don't edit the same file.

Update (04764c9, 955d29f), quality pass: merges the foundation fixes. A worktree inside the main checkout's directory made both it and the main worktree "active"; only the innermost one holding the shell's directory is current now (regression added). The design doc now states the key order while filtering (handleSearchKey before routeWorkspaceKey) and that changeDirectory is performed like /worktrees: directoryCommand(path) staged in an empty composer. The tmux escaping test expects an escaped escape sequence to be removed whole. CI green on 955d29f.