fix(tui): throttle re-renders, animate spinner, debounce resize, defensive emit

[Exelord]

Summary

Re-opening the perf/stability fix that didn't make it into the
merged PR #79. Same commit, addresses your "laggy and crashy and
freezing" report.

Four real bugs in the freshly-merged Solid TUI:

1. Reactivity firehose. pty-store called setRev() on every
   chunk. A chatty build tool (1k+ chunks/sec) triggered 1k+ Solid
   updates/sec, each re-running LogPane's memo which walked the
   entire xterm buffer. That's the lag.

   Fix: pty-store batches dirty = true on writes; a 30 Hz
   interval timer bumps the rev signal at most once per frame.
   pty-output.readLines() caches its result keyed by
   bytesWritten so an idle paint is O(1).

2. Spinner didn't animate. The createMemo over Date.now()
   only invalidates when its dependencies change; Date.now()
   isn't reactive. The spinner was frozen at whatever frame
   happened to render last.

   Fix: new ClockProvider context owns a single 10 Hz
   setInterval that updates a tick signal. TaskList's
   spinner memo reads tick() so it animates on every interval.

3. Resize cascaded. Every dim().width or height change
   resized every task's pty synchronously. OpenTUI can fire several
   resize events in a burst — freezing potential.

   Fix: 150 ms debounce in App.tsx — only resize ptys once
   after the resize storm settles.

4. Crashes propagated. A bug inside the runState reducer or
   pty handler would throw out of observer.emit, crashing the
   orchestrator.

   Fix: wrap each apply() call in observer.emit with
   try/catch; write errors to stderr but keep going. Same defense
   around the keyboard handler.

Plus a side bug: xterm-headless's window/self shim ran AFTER
the static import 'xterm-headless' due to Bun ESM hoisting
node_modules imports first. Replaced with a side-effect import of
xterm-shim.ts + a require() for the actual Terminal constructor
inside createPtyOutput.

Test plan

• bun src/bin.ts run ci — 3/3 pass (format-check + lint + 436 tests)
• Smoke test exercises the corrected path

If it's STILL bad after this lands, the painter problems are
OpenTUI's renderer itself, not our usage. The fallback path is the
hand-rolled cell-buffer + xterm-headless approach (Option A from
docs/design/tui-rebuild.md).

https://claude.ai/code/session_016HXj6HW6bxSn8EYuKcxTD9

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