feat(ui): add light theme toggle

[SirEdvin]

Status

Ready for maintainer review. This implementation was AI-assisted, then independently reviewed and verified with the project build and tests.

Summary

• Add a persisted dark/light theme provider using data-theme on the document root, keeping dark mode as the default.
• Add an accessible theme toggle to the shared top toolbar while preserving page-specific action slots.
• Add light-theme design tokens for app surfaces, text, borders, scrollbars, canvas grid, React Flow controls/minimap, rich text previews, shadows, and accent foregrounds.

Verification

• npm run build
• npm test
• npx eslint src/components/theme/ThemeProvider.tsx src/components/theme/ThemeToggle.tsx src/components/theme/theme-context.ts src/components/nav/PageToolbar.tsx

Note: full npm run lint still reports pre-existing lint errors elsewhere in the app; the files touched by this PR pass targeted ESLint.

[SirEdvin]

Light theme cleanup update

Pushed a follow-up pass that fixes the remaining light-theme mismatches from the screenshots:

• Agent settings tables/forms now use theme surfaces instead of hard-coded dark neutral panels.
• Create diagram modal and shared modal shells now use semantic theme tokens.
• Legacy dark card/table/form utility classes are remapped in light mode so older pages no longer render black islands on the light canvas.
• Disabled primary buttons now stay readable in light mode instead of fading coral text into a peach background.
• Docs/legal, Objects, and Connections surfaces were converted to theme tokens.

Verification:

• Browser/Playwright visual smoke in light mode across /agents-settings, /diagrams + create modal, /objects, /connections, /members, /teams, /versions, /drafts, /activity, /invites, /docs, and /terms found no remaining dark surface islands in the inspected viewport.
• Screenshot review confirmed the agent settings table, create diagram modal, members, connections, and legal pages are coherent/readable in light mode.
• npm test passed: 23 files, 175 tests.
• npm run build passed.
• Targeted ESLint on changed files passed.

Updated private registry images:

• registry.siredvin.home/archflow-backend:0.1.0-light-theme-04db637
• registry.siredvin.home/archflow-frontend:0.1.0-light-theme-04db637
• registry.siredvin.home/archflow-backend:light-theme-latest
• registry.siredvin.home/archflow-frontend:light-theme-latest

Frontend image smoke: nginx served the SPA root and expected title.

[SirEdvin]

Search modal light-theme fix

Pushed a follow-up for the search popup: SearchModal no longer uses hard-coded #171717/#333/#262626 inline styles. The modal, input, result rows, headings, hover/focus states, borders, and text now use the same semantic theme tokens as the rest of the app.

Verification:

• Browser/Playwright opened the app in light mode, clicked Search, typed pay, and captured the modal.
• Computed styles confirmed the modal background is light (rgb(255, 250, 242)), text is dark/readable, and no dark child surfaces were detected.
• Screenshot review confirmed the popup is now coherent/readable in light mode.
• npx eslint src/components/nav/SearchModal.tsx passed.
• npm test passed: 25 files, 180 tests.
• npm run build passed.

Updated private registry images:

• registry.siredvin.home/archflow-backend:0.1.0-light-theme-867bae8
• registry.siredvin.home/archflow-frontend:0.1.0-light-theme-867bae8
• registry.siredvin.home/archflow-backend:light-theme-latest
• registry.siredvin.home/archflow-frontend:light-theme-latest