docs: add adaptive light and dark Mermaid themes

[sirmrdrgod]

Summary

• replace the GitHub-rendered Mermaid block in docs/Architecture_Transition.md with transparent light and dark SVG variants selected through prefers-color-scheme
• preserve the full hybrid withdrawal graph in paired editable Mermaid sources
• keep WalletWall palette roles readable across GitHub default, color-vision, and soft-dark appearances without relying on color alone
• add full-size SVG links for narrow-screen inspection
• bump the package version from 0.10.4 to 0.10.5 for the repository PR version gate

Why

GitHub renders Mermaid diagrams on its own dark iframe background. The diagram SVG itself is transparent, so a single styled Mermaid block cannot control that surrounding canvas. GitHub supports appearance-aware images through a Markdown <picture> element, allowing transparent WalletWall light and dark variants while leaving diagram meaning unchanged.

Validation

• npm test -- test/DocsBoundary.test.ts — 9 passing
• npm run format:check — passed
• npx tsc --noEmit — passed
• npm run lint — 0 errors; existing warnings only
• git diff --check — passed
• browser rendering at 1440px and 390px — both variants render all 14 nodes and 3 boundaries with transparent backgrounds, no clipping, and no console errors
• Mermaid source parity check — graph structure identical between variants
• contrast check — node text pairs meet at least 4.5:1

Scope

Documentation presentation only. No contracts, APIs, application behavior, wallet flows, deployment logic, or generated build artifacts changed.