Redesign README and benchmark visuals

[sohams25]

What this changes

• README information hierarchy rebuilt: banner, minimal badge row, one-paragraph summary, result callout, visual result summary, single primary table, "why early exit lost here", architecture diagram, compact reproduction with details blocks, HTP proof chain, live/thermal section, camera-path note, layout, evidence links.
• New visual identity: three hand-authored SVGs (assets/banner.svg, assets/result-summary.svg, assets/architecture.svg) using the same four-color model coding as the committed charts; dark-neutral with one coral accent; renders on light and dark GitHub themes with descriptive alt text.
• Architecture diagram now shows the real final path (laptop webcam → MJPEG → USB ADB → on-board decode/preprocess/queue/runner/telemetry) with the CSI path marked unavailable.

What this does not change

• No benchmark data, raw results, or summary values changed — every displayed number re-verified against benchmarks/summary.json and benchmarks/accelerator_proof.json.
• No runtime or application code changed.
• Camera-path wording, measurement-boundary explanations (3.3 ms vs ~180 fps), negative results and limitations preserved.
• v0.1.0 tag and Release untouched.

Verification

• 23/23 unit tests pass; charts regenerate deterministically from committed raw data.
• Relative links and image references validated; SVGs are well-formed XML; rendered output inspected at desktop and mobile widths.
• Privacy scan clean.