feat(gui): route embedded TUI through dashboard gateway

[OutThisLife]

Summary

• set HERMES_TUI_GATEWAY_URL in dashboard PTY sessions so embedded ui-tui can attach to the in-process /api/ws gateway
• add _build_gateway_ws_url() helper and keep sidecar event fanout wiring unchanged for dashboard sidebar compatibility
• add web-server coverage to assert gateway URL injection in _resolve_chat_argv

Test plan

• scripts/run_tests.sh tests/hermes_cli/test_web_server.py -k "resolve_chat_argv_injects_gateway_ws_url or channel_param_propagates_sidecar_url"
• scripts/run_tests.sh tests/hermes_cli/test_web_server.py -k "PtyWebSocket or resolve_chat_argv_injects_gateway_ws_url"

[github-actions]

⚠️ npm lockfile hash out of date

Checked against commit db84eea (PR head at check time).

The hash = "sha256-..." line in these nix files no longer matches the committed package-lock.json:

• nix/web.nix:8 (.#web): sha256-HWB1piIPglTXbzQHXFYHLgVZIbDb60esupXSQGa1+lI= → sha256-jJsVp3Dz+6/GaruxcUSby+G1vVB+nHHlu1tFWE9wQZQ= — lockfile: apps/dashboard/package-lock.json

Apply the fix

• Apply lockfile fix — tick to push a commit with the correct hashes to this PR branch
• Or run the Nix Lockfile Fix workflow manually (pass PR #21975)
• Or locally: nix run .#fix-lockfiles and commit the diff

[OutThisLife]

Superseded by #21978 (core TUI attach to main) and #21979 (bb/gui wiring).