terminals: resize with the panel, and five xterm addons

The terminal was xterm with one addon (fit) and a single fit() call at connect, so the
shell kept whatever cols/rows it was born with. Drag a panel wider and the PTY never
heard about it — anything drawing a full screen (an agent TUI, top, vim) rendered into a
box that no longer matched the one you were looking at. A ResizeObserver now refits and
sends pty:resize, coalesced to one fit per frame because dragging an edge fires
continuously and each fit reflows.

Scrollback goes from xterm's default 1000 lines to 10,000 — one long agent turn was
enough to lose the start of it.

Addons, all off the shelf and none previously loaded:

- webgl — the renderer, and the reason fast repainting feels smooth rather than syrupy.
  Guarded twice: construction can throw where there is no GL context, and the context can
  be lost later, so both paths fall back to the DOM renderer instead of a dead canvas.
- unicode11 (+ allowProposedApi) — correct widths for emoji, CJK and box-drawing. The
  default unicode 6 tables are why agent TUI frames sit a column out.
- web-links — URLs in output are clickable.
- search — with a find bar on Ctrl/Cmd-Shift-F. Not plain Ctrl-F: that is forward-one-char
  in readline and emacs, and swallowing it would break every shell in the app.
- serialize — installed for exact-state replay, not yet wired.

Also reports the shell's own title (OSC 0/2) and the bell through new optional callbacks,
so a panel can show what is running in it and flag a finished turn you weren't watching.
Nothing consumes them yet.

Unrelated but found by this run: three origin-validation tests were failing. Not from this
change — ALLOW_ANY_ORIGIN=true in .env, added last night, and Bun loads the host .env into
tests, so the kill switch had silently turned the assertions into no-ops. The test now pins
both escape hatches off, since its whole job is asserting the checks reject things.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/servers/_middlewares/origin-validation.test.ts

@@ -3,6 +3,11 @@ import { test, expect } from 'bun:test';
 // origin-validation reads PUBLIC_URL / PUBLIC_BUILD_ENV at module load, so set them before importing.
 process.env.PUBLIC_URL = 'https://officer.example.com';
 process.env.PUBLIC_BUILD_ENV = 'production';
+// Bun loads the host's .env into tests, so an operational kill switch left on there would silently turn
+// these assertions into no-ops — which is exactly what ALLOW_ANY_ORIGIN=true did. Pin the escape hatches
+// off: this file's whole job is asserting that the checks reject things.
+process.env.ALLOW_ANY_ORIGIN = 'false';
+process.env.ALLOW_ANY_ORIGIN_MUSIC = 'false';
 
 const { isOriginAllowed } = await import('./origin-validation');