feat(keep): import annotations

[markoub]

Summary

• Imports Google Keep annotations from exported JSON notes instead of dropping them.
• Appends annotations as a small Markdown ## Annotations section at the end of the note.
• Formats web annotations as links when a URL is present, includes descriptions when available, and ignores empty annotation objects.

Closes #258

Notes

The issue discussion suggested a list at the end of the note because Keep annotations are note-level metadata rather than ranges tied to specific note text. This keeps the imported note readable while preserving the exported link metadata.

This does not change attachment handling, timestamps, duplicate handling, or HTML imports.

Validation

• pnpm install --frozen-lockfile
• pnpm exec tsx --test tests/keep/annotations.test.ts
• pnpm run test
• pnpm run build
• pnpm exec eslint src/formats/keep-json.ts src/formats/keep/models.ts src/formats/keep/util.ts tests/keep/annotations.test.ts
• git diff --check origin/master...HEAD