fix(ui/text): stop idle 300ms re-render loop that could OOM the TUI

[michaelneale]

Problem

The Ink-based text UI (ui/text) could crash with a JS heap OOM after running for a while, even when it appeared idle:

FATAL ERROR: Ineffective mark-compacts near heap limit
Allocation failed - JavaScript heap out of memory

The native stack showed the crash happening inside a libuv check tick (uv__run_check → Builtins_JSEntryTrampoline), i.e. a JS timer callback — which pointed at the 300ms animation interval in App.

Root cause

ui/text/src/tui.tsx had this at the top of App:

useEffect(() => {
  const t = setInterval(() => {
    setSpinIdx((i) => (i + 1) % SPINNER_FRAMES.length);
    setGooseFrame((f) => f + 1);   // never wrapped
  }, 300);
  return () => clearInterval(t);
}, []);

Two problems compound:

1. gooseFrame was incremented without modulo, so state changed every tick even when the splash goose wasn't being shown.
2. The interval ran for the entire lifetime of the process regardless of whether anything was actually animating. That forced a full re-render of App every 300ms forever.

Each of those re-renders called buildContentLines(...), which walks every turn's responseItems and runs marked + marked-terminal over every streamed content_chunk from scratch, allocating thousands of fresh Ink/Yoga elements per tick.

In a long-running session with a substantial transcript this is roughly O(total_chars_streamed) of markdown parsing ~3× per second, indefinitely. Young-gen fills, promotions pile up, mark-compact can't keep up, and V8 eventually gives up at the 4GB heap cap.

This affects real npx @aaif/goose users, not just dev — dev just hits it faster because of tsx transpile overhead on top.

Fix

1. Only tick when something is animating. The animation useEffect now bails unless bannerVisible (splash goose) or loading (spinner) is true. Once the user dismisses the banner and is sitting at the prompt, the interval is cleared entirely and the UI stops re-rendering on its own.
2. Wrap gooseFrame with modulo GOOSE_FRAMES.length so state doesn't change when the banner isn't visible, and doesn't drift monotonically when it is.
3. Memoize buildContentLines via useMemo so any re-renders that do happen (e.g. window resize, new chunk) don't needlessly re-parse markdown for historical turns.

Verification

• tsc --noEmit (the package lint script) passes.
• Manually: leaving the TUI open at the prompt no longer grows RSS over time; previously it climbed steadily.

Notes

I also wrote up a longer dev-experience audit of ui/text (README drift, stderr: 'ignore' swallowing backend errors in dev, missing watch mode, etc.). Happy to do those as a follow-up if useful — this PR is scoped to the OOM fix.