02: finish design-contract alignment on application surfaces #343

Part of #341.

What to build: finish the design-contract alignment on application surfaces: sweep for radius/shape-hierarchy violations, unapproved rounded-2xl usage, and overlay-role drift against apps/pythinker-web/DESIGN.md, and fix every real violation onto the contract tokens. Verify every token-driven change in all four appearances: light, dark, system-dark, and the mono accent.

Blocked by: #1 (audit runs on the merged tree).

Status: in-flight

• rg 'font-size:\s*[0-9]' apps/pythinker-web/src --glob '*.vue' shows no application-text hits outside DesignSystemView and the documented glyph exemptions
• Radius/shape/2xl/overlay violations on application surfaces are zero outside documented exceptions (recorded rg/inspection evidence)
• No visual regression by inspection in light, dark, system-dark, mono accent (token scoping reviewed per change)
• Web typecheck + build green; dist-web restaged if src changed

Demo path: the rg evidence lines plus the per-change token mapping table in the ticket receipt.

Claims amended: +apps/pythinker-code/dist-web/ (shared-regenerate): any web src edit forces the bundle restage through pnpm run build:web
Capability: standard/medium
Claims: exclusive: apps/pythinker-web/src/components/, apps/pythinker-web/src/style.css, apps/pythinker-web/DESIGN.md ; shared-regenerate: apps/pythinker-code/dist-web/