feat(text): publish warm generations in object lifecycle

[thejustinwalsh]

Summary

• stage resident font, shaping, layout, paint, and raster updates synchronously while preserving the last committed generation
• publish prepared generations from updateMatrixWorld / updateWorldMatrix before raster-child traversal, with React invalidating its R3F root instead of awaiting ready
• retain one Presentation canvas and renderer across workload, technique, font, and DPR handoffs; remove Icon Grid's hide-and-await recycle path
• keep ordinary Text Ladder content visible, preserve the timed-demo exit, and suppress the temporary zero-vertex WebGPU grid draw
• make the DPR-2 workload probe capture-free during cadence sampling, then take one bounded headless pixel proof so Chromium screenshot compositing cannot flash the visible canvas

Verification

• pnpm --filter @pmndrs/text-benchmarks test:unit — 45 files, 260 tests; script tests 4/4
• pnpm --filter @pmndrs/text-benchmarks test:headless — all 19 conformance cases pass together, including 3/3 exact React reconciliations and 3/3 exact 68-frame Advanced Shaping timelines
• pnpm --filter @pmndrs/text-benchmarks test:packed — exact packed-consumer hash and 172,156-byte output
• pnpm --filter @pmndrs/text-benchmarks test:presentation-workloads — all seven DPR-2 workloads retain one canvas/renderer with visible foreground pixels; Bitmap, MTSDF, and Slug lanes pass
• pnpm --filter @pmndrs/text-benchmarks test:presentation-demo — timed DPR-2 demo completes, returns to Off-axis / 3D, retains one renderer, and reports 60.02 FPS during Icon Grid with no warnings
• focused Text, React, retained-scene, canvas, and persistent-host lifecycle tests — success, failure, abort, stale work, sibling traversal, and state restoration pass
• package-size and autoresearch checks — exact; baker hosts and Wasm unchanged
• pnpm docs:check — zero conformance errors, producer-profile errors, or warnings
• repository formatting and diff checks — clean

Depends on #12.