fix(registry): position flowchart typing beats with label-relative offsets

[jurczykpawel]

Fixes #2548.

What

registry/blocks/flowchart/flowchart.html and registry/blocks/flowchart-vertical/flowchart-vertical.html schedule the "Pythom" → "Python" typing correction by reading a label position back off the timeline (const typingStart = tl.labels["hold5"]). The render compiler executes composition scripts under a GSAP proxy whose timeline exposes no readable .labels map, so the script throws before window.__timelines is assigned — the block is never registered, renders capture only the dotted-grid background, and every render pays the 45 s sub_timeline_readiness_timeout.

How

Position the typing beats with GSAP's label-relative syntax (`hold5+=${i * 0.05}`) — the same idiom every other step in these files already uses ("hold1+=0.25", "hold6+=0.3", …). typingEnd becomes a relative offset and hold6 is added as `hold5+=${typingEnd + 0.5}`. Timing is byte-identical to the authored intent; no .labels read remains.

Verification

• npx hyperframes@0.7.60 render of a composition mounting flowchart-vertical in a 3 s window:
  • before: blank dotted grid for the whole window + sub_timeline_readiness_timeout (+45 s on every render), browser console shows [Compiler] Composition script failed … reading 'hold5'
  • after: the flowchart animates through its full sequence; no compiler error; the readiness timeout disappears (render time drops accordingly)
• Verified on macOS arm64 (native) and linux/amd64 (Docker).
• bun run lint and bun run format:check pass.