feat(seo): add PWA web app manifest and theme-color metadata

[AbuJulaybeeb]

What was done Implemented a web app manifest for installability, PWA integration, and richer platform/OS metadata.

PWA Web App Manifest: Created src/app/manifest.ts using the Next.js MetadataRoute API. It returns name, short_name, description, start_url, display type, and theme/background colors aligned with the Light/Dark palettes defined in src/app/globals.css.
Favicon Integration: Configured the manifest to point to the existing src/app/favicon.ico.
Apple Touch Icon and Metadata Wire-up: Updated src/app/layout.tsx to set manifest to /manifest.webmanifest, specify an apple touch icon mapping /favicon.ico in the metadata, and export a viewport configuration containing the responsive media query-based theme color declarations.
Documentation: Documented the PWA/manifest support in README.md under the SEO section.
Unit Testing: Created src/app/manifest.test.ts to assert that all required manifest keys are present, the configured colors match the palette, and the favicon is registered. Updated src/app/layout.test.tsx to assert viewport and manifest properties.
How it was verified

Checked linting and typecheck:
bash
npm run lint && npm run typecheck

Output: Done with 0 errors

Ran isolated tests with 100% coverage on manifest.ts:
bash
npx jest src/app/manifest.test.ts --coverage --collectCoverageFrom=src/app/manifest.ts

Output:

-------------------|---------|----------|---------|---------|-------------------

File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s

-------------------|---------|----------|---------|---------|-------------------

All files | 100 | 100 | 100 | 100 |

manifest.ts | 100 | 100 | 100 | 100 |

-------------------|---------|----------|---------|---------|-------------------

Test Suites: 1 passed, 1 total

Tests: 1 passed, 1 total

Verified metadata and viewport test suite:
bash
npx jest src/app/layout.test.tsx

Output: PASS (2 passed)

closes #89

[mikewheeleer]

solid — thanks for picking it up 🙌