examples/compose: build ttyd from our fork with autoreconnect patch

[hndrewaall]

Summary

The ttyd web console in examples/compose/ previously served the upstream
tsl0922/ttyd:1.7.7 image's embedded HTML directly. That HTML's WebSocket
client only reconnects on non-1000 close codes and bails entirely after a
single socket error event, so laptop sleep / VPN flap / brief network
drops park the in-browser terminal at "Press Enter to Reconnect" until
someone notices.

This PR adds a node-based frontend-builder stage that clones our ttyd
fork (https://github.com/hndrewaall/ttyd) and runs yarn build +
gulp inline against it, producing a single self-contained HTML file
that ships:

• exponential-backoff auto-reconnect (1s -> 30s) on every close while
  reconnect is enabled, not just non-1000 codes
• reconnect kept enabled across error events (the always-following
  close drives the retry)
• a visibilitychange handler that cancels any pending backoff and
  reconnects immediately when the tab becomes visible
• backoff reset on a successful (re)open

The autodark CSS + theme-swap inject-autodark.py pipeline still runs on
top of the fork-built HTML. The upstream ttyd C binary is unchanged —
we still copy it out of tsl0922/ttyd:1.7.7.

The fork pin is captured as TTYD_FORK_REF (defaults to the squash-merge
SHA on the fork's main). Once the upstream PR
tsl0922/ttyd#1536 merges,
the pin can move back to a tsl0922/ttyd tag.

Test plan

• Local sudo docker build examples/compose/ttyd/ succeeds end-to-end.
• Resulting image contains the autoreconnect identifiers in
  /usr/local/share/ttyd/index.html (visibilitychange,
  scheduleReconnect, reconnectDelay, reconnectMaxDelay,
  installVisibilityHandler all present).
• Autodark inject still applies (prefers-color-scheme + autodark-injected
  grep matches preserved as build-time guards).
• Cold-start the full docker compose up stack; tab into
  http://localhost:7681 and verify reconnect overlay appears after a
  forced socket close instead of "Press Enter to Reconnect".