feat: v0.6.0 light mode, command palette, dialogs, toasts

- Light mode with the house ☀/◐ toggle and lt_theme preference; light
  terminal palette; Claude runs with dark-ansi so its colours follow the
  palette; tmux and the statusLine use ANSI colours.
- Command palette (⌕, Ctrl+Shift+P) with session, terminal, view, link and
  help commands.
- .lt-modal dialogs for new/rename/end and a keyboard shortcuts sheet.
- .lt-toast results for actions, uploads, copy and CI.
- ttyd dropped the reply of fast one-shot commands; replies now wait for the
  browser to hang up, and the client hangs up as soon as it has one.
- Sessions panel re-fetches after an action instead of reusing a stale poll.

Closes #31
Closes #32
Closes #33
Closes #34
Closes #35

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

libexec/devdesk-serve

@@ -22,4 +22,7 @@ if [ -n "${DEVDESK_BIND:-}" ]; then
     args+=(--interface "$DEVDESK_BIND")
 fi
 
+# Tells `devdesk attach` it talks to a browser through ttyd (see dd_linger).
+export DEVDESK_VIA_TTYD=1
+
 exec "${DEVDESK_TTYD:-/usr/lib/devdesk/bin/ttyd}" "${args[@]}" "${DEVDESK_BIN:-/usr/bin/devdesk}" attach