Claude Code engine, image viewer, colour tags, checks per turn and more

- Claude Code as an engine: chats on a "claude-code/<alias>" model run through
  the claude CLI (stream-json); tool approvals go through our permission
  system. Sign in from the web UI (URL + pasted code), CLI version and update
  from Settings; the Docker image contains the CLI.
- Small models (8k context) for side tasks: input is cut to the model's
  context window; one-line chat status, "What does this do?" on approvals,
  "Plan as automation" (job draft from a chat).
- Mobile: top bar no longer widens the page, image viewer (zoom, swipe, mark
  up, use in message), jump to previous own message, message menu, time under
  every message.
- Approvals: push actions (allow/reject), "always allow in this project"
  (never for dangerous commands) with revoke.
- Per turn: changed files with diffs and rollback; project check command with
  a green/red badge and "let the agent fix it".
- Colour tags for chats in the colours of the active theme.
- Project defaults for new chats, project page (timeline), offline queue.

Tested in a throwaway container with a mock model (8k small model): 26 API
checks passed (permissions, diffs, checks, defaults, job draft, side-task
budget, Claude Code status/login URL, unsigned-in chat).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

web/src/components/NewSession.tsx

@@ -328,7 +328,8 @@ export function NewSession({ onMenu, onCreated }: { onMenu: () => void; onCreate
       const isCraft = task === "craft";
       const s = await post<{ id: string }>("/sessions", {
         cwd,
-        model: model || undefined,
+        // The server default is not sent, so the project's own default model can apply.
+        model: model && model !== config?.default_model ? model : undefined,
         agent: task === "cad" ? "build" : task,
         clean_room: isCraft ? !deep : undefined,
       });