COD-107 remote SSH: custom port + advanced connection options (escape hatch)

The Remote case form could only reach port-22, default-identity, directly
SSH-able hosts. Add an escape-hatch set of SSH connection options so Codeman
can reach a host like aa-desktop (custom port 2222, ed25519 identity, cloudflared
SOCKS5 ProxyCommand) the way ssh-aa-desktop does — without shelling out to that
wrapper.

- Model (types/session.ts): new optional RemoteSshOptions (identityFile,
  socksProxy, jumpHost, extraSshOptions) on RemoteHost AND SessionRemote; all
  absent = today's behavior. toSessionRemote() carries them case->session.
- Shared buildSshConnectionArgs(remote) in remote-hosts.ts: pure, exported,
  ordered ssh connection tokens (-o BatchMode=yes, -p, -i <abs identity with
  ~/$HOME expanded + shellescaped>, -J, -o ProxyCommand=nc -X 5 -x <socks>
  %h %p emitted as ONE shellescaped token so %h %p reach ssh literally, then
  each extraSshOptions -o). Both buildRemoteLaunchCommand (tmux-manager.ts) and
  buildRemoteTmuxCheckCommand now use it, so the prereq probe and the real
  launch connect identically. checkRemoteTmuxAvailable widened to accept the
  options (callers already pass the full host).
- Validation (schemas.ts): identityFile (no newline/NUL), socksProxy
  (host:port), jumpHost (no shell metachars), extraSshOptions (KEY=VALUE,
  reject newline/NUL/backtick/$() — defense-in-depth on operator-entered config.
- UI (index.html + session-ui.js): SSH Port field + collapsible "Advanced SSH"
  section (identity, SOCKS proxy, jump host, extra -o options one per line);
  wired into the remote-host create payload.

Empty-options remotes emit byte-identical ssh to before (pinned by test).

Tests: test/remote-ssh-options.test.ts (buildSshConnectionArgs +
buildRemoteLaunchCommand + buildRemoteTmuxCheckCommand for the aa-desktop set,
escaping/%h %p/identity-~ expansion, byte-identical back-compat); case-routes
schema tests (advanced options round-trip; malformed extraSshOptions/socksProxy
rejected). tsc/eslint/frontend-syntax/prettier/build clean.

Acceptance (real remote, no wrapper): the emitted command connected to
aa-desktop through the cloudflared SOCKS proxy and created a durable remote
tmux session (verified independently via ssh-aa-desktop: CONNECTED_NO_WRAPPER,
STILL_ALIVE_AFTER_DETACH); checkRemoteTmuxAvailable over the proxy returned
{ok:true, tmuxPath:/usr/local/bin/tmux}; test session cleaned up.

src/mux-interface.ts

@@ -17,6 +17,7 @@ import type {
   CodexConfig,
   EffortLevel,
   GeminiConfig,
+  SessionRemote,
 } from './types.js';
 
 /**
@@ -33,6 +34,8 @@ export interface MuxSession {
   createdAt: number;
   /** Working directory */
   workingDir: string;
+  /** Remote execution metadata for local tmux sessions wrapping SSH */
+  remote?: SessionRemote;
   /** Session mode */
   mode: SessionMode;
   /** Whether webserver is attached to this session */
@@ -74,6 +77,8 @@ export interface CreateSessionOptions {
   effort?: EffortLevel;
   /** tmux history-limit (scrollback lines) to set for this session. */
   historyLimit?: number;
+  /** Remote execution metadata for local tmux sessions wrapping SSH */
+  remote?: SessionRemote;
 }
 
 /** Options for respawning a dead pane. */
@@ -96,6 +101,8 @@ export interface RespawnPaneOptions {
   effort?: EffortLevel;
   /** tmux history-limit (scrollback lines) to set for this session after respawn. */
   historyLimit?: number;
+  /** Remote execution metadata for local tmux sessions wrapping SSH */
+  remote?: SessionRemote;
 }
 
 /**