docs(readme): refresh hero images and add performance section

[363045841]

Summary

Refresh the generated READMEs and their source fragments/templates.

Changes

• Hero images: replace all hero screenshots with the current set (indicator rendering/selection, 5-day line, mobile, comparison view, Agent).
• New Performance section (docs/fragments/_performance.md, _performance.zh-CN.md), wired into the root and Vue templates:
  • WebGPU command submission A/B (batched vs split queue.submit, 5.50× speedup).
  • MA5/MA20/MA60 (simple indicator) and Ichimoku (complex rendering workload) tables across Canvas2D/WebGL2/WebGPU at 1k/5k/10k visible K-lines (prepare/submit/GPU P50, FPS, 1% low, frame P99, jank).
  • Notes the self-developed rendering engine and its direct Canvas/WebGL/WebGPU primitive submission, plus a note that Ichimoku jank is a CPU-side bottleneck (not the rendering engine) to be optimized later.
• Roadmap: mark "advanced drawing tools" and "multi-period K-line display" as done.
• What's New: add v0.10 and v0.11 highlights.

Notes

• READMEs are generated: pnpm docs:generate; pnpm docs:check passes.
• All edits are in docs/fragments, docs/templates, and the regenerated READMEs.