COD-105 discover + attach existing remote tmux sessions (detach-not-kill)

Phase 2 of the remote-tmux arc. Discover codeman-* tmux sessions already
running on a remote host (created by the remote's own Codeman or another
instance) and attach to one this Codeman didn't launch, with detach-not-kill
ownership for non-owned sessions.

- remote-hosts.ts: listRemoteCodemanSessions (ssh, VITEST-guarded, never throws)
  + pure parseRemoteSessionList + buildRemoteListSessionsCommand. Parser splits
  on the LITERAL \t the remote tmux emits (next-3.7 does not expand \t) AND a
  real tab. toAttachedSessionRemote builds a non-owned SessionRemote; toSessionRemote
  now marks the COD-104 launch path owned:true.
- tmux-manager.ts: buildRemoteAttachCommand (sibling of buildRemoteLaunchCommand);
  buildRemoteSessionCommand selects attach vs launch by ownership. killSession gains
  a detach-not-kill early return for non-owned remote sessions: tears down only the
  LOCAL pane (kills local ssh -> remote attach detaches), NEVER issues a remote
  kill-session.
- types/session.ts: RemoteSessionInfo; SessionRemote.owned + remoteSessionName.
- schemas.ts: CreateSessionSchema.attachRemoteSession {hostId, remoteSessionName};
  fixed a pre-existing no-useless-escape lint error in the jumpHost regex.
- case-routes.ts: GET /api/remote-hosts/:hostId/sessions (explicit discovery).
- session-routes.ts: attachRemoteSession create path -> non-owned session.
- UI (index.html/session-ui.js/styles.css): explicit "Discover existing sessions"
  button + Attach action (owned:false). No auto-discover.

Verified on aa-desktop: discovered codeman-disco1, attached (attached=1, shared
view), killed local probe pane -> remote SURVIVED_DETACH (attached=0). Tests:
parse/attach-cmd/ownership unit + discovery route, session-routes + case-routes green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
(cherry picked from commit 55f5ada9db6d01518a4adf6b752e460b5df39524)

src/web/public/index.html

@@ -1915,6 +1915,17 @@
                 </div>
               </div>
             </details>
+            <!-- COD-105 — discover + attach existing remote tmux sessions this Codeman didn't create. -->
+            <details class="advanced-options" id="remoteDiscoverSection">
+              <summary>Discover existing sessions</summary>
+              <div class="advanced-options-content">
+                <span class="form-hint">Find <code>codeman-*</code> tmux sessions already running on this host (started by the remote's own Codeman or another instance) and attach to one. Attaching shares the session; closing the tab detaches it — it is never killed.</span>
+                <div class="form-row" style="margin-top: 8px;">
+                  <button type="button" class="btn-toolbar" id="remoteDiscoverBtn" onclick="app.discoverRemoteSessions()">Discover existing sessions</button>
+                </div>
+                <div id="remoteDiscoverResults" class="remote-discover-results"></div>
+              </div>
+            </details>
           </div>
           <!-- Manage Tab -->
           <div class="modal-tab-content hidden" id="case-manage">