feat(terminal): resolve relative path links against the pane's current directory

A relative path printed in the terminal was resolved against the session's
workingDir, which is fixed at create time and never follows a cd. In a shell
that moved into a subdirectory or a sibling repo, the link opened the wrong
file or reported "File not found".

The pane-exit watcher's batched list-panes read already carries
#{pane_current_path}. derivePaneCurrentPaths() turns those rows into one
directory per single-pane session, TmuxManager.getPaneCurrentPath() serves it
from memory, and the server applies it on the existing paneExitsUpdated tick
as SessionState.cwd, broadcasting only on a change. No new tmux call, no new
SSE event. A failed read keeps the previous answers.

Session.setCwd() uses the paneExit scoping rule: remote and Docker sessions
never get a cwd (their local pane runs the ssh or docker exec client), nor do
direct-PTY or rediscovered sessions. The value is runtime-only.

In the browser, relativeResolutionBase() picks the live cwd when known and
workingDir otherwise. It only changes the base a relative path joins: the
result is routed as before, so a target outside the workspace still goes
through the attachment routes, and file-content/file-raw are unchanged.

src/types/session.ts

@@ -834,6 +834,19 @@ export interface SessionState {
   status: SessionStatus;
   /** Working directory path */
   workingDir: string;
+  /**
+   * The directory the session's local tmux pane is in NOW (`#{pane_current_path}`),
+   * when known. `workingDir` is fixed at create time and never follows a `cd`;
+   * this is what a relative path printed in the terminal is relative to.
+   *
+   * Runtime-only: refreshed from the pane-exit watcher's read and never restored
+   * from disk, so a restart starts blank. Absent for remote and docker sessions
+   * (their local pane runs the ssh / docker-exec client) and for direct-PTY or
+   * rediscovered sessions. NOT a confinement root: the file routes stay confined
+   * to `workingDir`, and a path resolved outside it goes through the attachment
+   * routes like any other out-of-workspace path.
+   */
+  cwd?: string;
   /** Remote execution metadata, present when this session runs over SSH through local tmux */
   remote?: SessionRemote;
   /** Docker execution metadata, present when this session runs inside a container via local tmux + docker exec */