implement builtin.claude per D-041

Tier-0 stub flipped to the real Claude pane. Primary-per-repo
semantics: session name is `clide-claude-<hash>` where <hash> is
FNV-1a over the workspace root path, so reopening clide attaches
to the same `claude` process through `tmux new-session -A`.

Primary has no close button — closing the tab disposes the widget
but deliberately does NOT call pane.close, so the tmux session
survives until the user actually exits claude or clide is shut
down. Secondary sessions (spawned via the claude.new-secondary
command registered here, UI wiring lands next) close normally and
the pane.close cascades into tmux kill-session.

Graceful fallback when tmux isn't on PATH: retries the spawn with
argv=['claude'], surfaces "no-tmux · fresh every launch" in the
header subtitle so the user knows persistence is off.

Session-naming unit tests cover determinism + uniqueness per repo.
Full app suite: 174 tests passing.

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

app/lib/kernel/src/i18n/catalog/builtin.claude_en_us.json

@@ -0,0 +1,7 @@
+{
+  "tab.title": { "translation": "Claude" },
+  "status.attaching": { "translation": "attaching…" },
+  "status.no-tmux": { "translation": "no-tmux · fresh every launch" },
+  "status.exited": { "translation": "session exited" },
+  "status.primary-exited": { "translation": "session exited — restart clide to retry" }
+}