fix(deepseek): review-driven hardening across the harness integration

Fifteen review findings on the dsh mode, the serious ones first:

- Multi-user: DEEPSEEK_BASE_URL joins the owner-clamped env keys.
  _configureDeepSeek() forwards the SERVER's own DEEPSEEK_API_KEY into
  every dsh pane and applyEnvOverrides() lands after it, so a non-granted
  owner who could redirect the base URL would have the operator's key sent
  as a bearer credential to a host of their choosing.
- Wait registry: until=stop/blocked is refused on docker and remote-SSH
  dsh sessions (new deepSeekBridgeUnreachable fact in sessionHookOptions).
  The HERDR triple is set via LOCAL tmux setenv, which crosses neither
  docker exec nor ssh, so such a session can never post a hook event and
  the wait burned its whole timeout on every turn.
- Approvals: a dsh item is an ALERT, not an answerable card. The answer
  route refuses (the '1'/Esc keystrokes are Claude-dialog-shaped and the
  option parser cannot read a third-party TUI's frames, so an answer was a
  blind keystroke into a foreign composer), and the push notification
  carries no Approve/Deny actions for dsh sessions.
- Status shim (v3): --seq is forwarded and the server drops stale retried
  reports inside a 60s window (the TUI retries with backoff, so a retried
  'working' could land after 'blocked' and resolve an approval whose
  dialog was still on screen); 4xx responses exit 0 instead of retrying,
  so one misconfigured session cannot feed the auth rate-limit bucket
  until the hook endpoint 429s for the whole instance.
- Web-UI server: concurrent starts are serialized through a lock (two
  racing POSTs used to pick the same port and orphan the winner), and the
  readiness poll / timeout paths only clear or stop the singleton while it
  is still theirs. First click actually opens the tab now
  (refreshWebviews, not the nonexistent loadWebviews). DELETE
  /api/deepseek/web requires the privileged grant in multi-user mode.
- Cron: deepseek jobs run the same two-part launch gate as the HTTP
  create paths (impl moved into the resolver so all three share it) and no
  longer stamp a Claude default model on the session.
- Parity sweeps: quick-start's docker branch rejects deepSeekConfig like
  the remote branch; the Ralph auto-enable list gained deepseek;
  HookEventType gained agent_working; the phone overview run menu filters
  managed webview records like the desktop menu.
- install.sh: the dsh identity probe closes stdin (under curl|bash a
  child that reads stdin eats the rest of the script), bounds the exec
  with timeout where available, and is memoized to one scan per install.
- Welcome screen: .welcome-btn-deepseek styled in the #4d6bfe brand
  identity (it rendered as an unstyled UA-grey button); stale markup
  comment about the web shortcut rewritten; clamp docs updated.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/utils/deepseek-cli-resolver.ts

@@ -363,3 +363,39 @@ export function getDeepSeekCliVersion(): string | null {
 export function profileExists(name: string): boolean {
   return existsSync(join(resolveDshHome(), 'profiles', name, 'package.json'));
 }
+
+/**
+ * Why a DeepSeek session cannot start, or null when it can.
+ *
+ * Availability for this mode is TWO questions, not one, because `dsh` is a
+ * profile launcher rather than an agent: the binary must resolve (and prove it
+ * is the harness and not Debian's dancer's shell), AND a profile that can occupy
+ * a pane must exist. Every create path — both HTTP routes AND cron fires — must
+ * ask this before constructing a Session, or the pane boots the box's default
+ * profile, which may be a logging web server or a one-shot that exits on
+ * arrival, and the prompt is typed into it.
+ */
+export function resolveDeepSeekLaunchError(requestedProfile?: string): string | null {
+  if (!isDeepSeekAvailable()) return getDeepSeekNotFoundMessage();
+
+  const profiles = listDeepSeekProfiles();
+  if (requestedProfile) {
+    const match = profiles.find((p) => p.name === requestedProfile);
+    if (!match) {
+      return `DeepSeek Harness profile "${requestedProfile}" does not exist. Create it with: dsh plugin --profile ${requestedProfile} add <package>`;
+    }
+    if (match.kind === 'web' || match.kind === 'headless') {
+      return `DeepSeek Harness profile "${requestedProfile}" is a ${match.kind} profile and cannot run in a terminal session. Pick an interactive profile, or open the web profile as a Codeman web tab.`;
+    }
+    return null;
+  }
+
+  if (!resolveDefaultDeepSeekProfile(profiles)) {
+    return (
+      'No interactive DeepSeek Harness profile is installed. DeepSeek ships only the web and headless ' +
+      'profiles, so the terminal agent comes from a plugin — install one with: ' +
+      'dsh plugin --profile dsh-tui add @deepseek-harness-tui/dsh-tui'
+    );
+  }
+  return null;
+}