feat(viewer): the agent dock and the first-run page (P11b)

D-27: a terminal panel along the bottom of the viewer (alacritty_terminal over
a PTY) runs Claude Code (default) or Codex in the book's books home, resizable,
collapsible, the choice remembered. The agent is an ordinary child process the
owner describes (agent_start); the viewer stays read-only: the agent writes
through the server like any other. A missing agent is offered through its
vendor's installer (a command to copy), never bundled; no folder is marked
trusted (Q-7, recommended answer: let Codex ask). Windows is not offered until
its ConPTY checks are recorded.

P11a found that onboarding with no terminal was false: the viewer opened only an
existing book. With no books and an owner, wanderbooks gui now shows a first-run
page: the private folder, the owner passphrase (typed in the viewer, optional),
the first books, an agent, then the books open. connect and New books... make
the books home. Tests: dock.rs, welcome.rs, books_home.rs (host and cli).
Docs: testing.md record and For P12, architecture, parity, gui.md, README.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

README.md

@@ -93,7 +93,13 @@ curl -fsSL https://wanderbooks.ai/install.sh | sh -s -- acme
 Already installed, three commands: `wanderbooks setup`, `wanderbooks books
 create acme`, `wanderbooks connect claude --book acme` (or `connect codex`).
 Then talk to the agent; `wanderbooks gui acme` shows the books, and its
-Books menu backs them up, restores, starts new books and closes them.
+Books menu backs them up, restores, starts new books and closes them. With
+no terminal (the AppImage, a menu entry), opening the app with no books
+shows a first-run page that does the same three steps (the private folder,
+an owner passphrase, the first books) and connects an agent; a panel along
+the bottom of the window then runs Claude Code or Codex in the books' own
+folder, `~/Documents/Wanderbooks/<id>` (optional: any agent can use the
+books).
 
 Updating: an AppImage, or a `wanderbooks` you put somewhere yourself, brings
 itself to the newest release with `wanderbooks update` (it checks the