feat: add keeply export command

[RolfKoenders]

Summary

• New keeply export command — no equivalent existed before
• Supports --format json (default) and --format html for Netscape browser import
• Outputs to stdout by default (composable: keeply export | jq '.[].url')
• --output <file> writes to disk and prints Saved to <file> to stderr
• --include-trashed flag to include soft-deleted bookmarks
• Uses raw fetch with ApiKey auth header (rather than KeeplyApi.request() which always calls .json())
• Helpful error when no API key is configured, pointing to keeply config set-key
• 9 tests in export.spec.ts covering all flags, stdout/file modes, API errors, and missing config

Test plan

• npx tsc --noEmit — clean
• npm test — all 59 tests pass including 9 new export tests
• keeply export — streams JSON to terminal
• keeply export --format html --output bookmarks.html — writes file, prints "Saved to bookmarks.html"
• keeply export | jq '.[].url' — works as pipe

Closes Keeply-link/docs#3

[RolfKoenders]

Overall solid implementation with good test coverage. One issue:\n\n****: The entire file was reformatted from single quotes to double quotes, creating a noisy diff. This makes it hard to see the actual functional change (adding ). Please revert the quote-style changes to match the existing file style, or split the formatting into a separate commit.\n\nOther minor notes:\n- Consider adding a timeout on the call for large exports.\n- The mutation pattern in tests works but is slightly fragile if tests ever run in parallel.\n\nPlease fix the quote churn in and I'll approve.

[RolfKoenders]

Review: Needs minor fix\n\nOverall solid implementation with good test coverage. One issue:\n\n****: The entire file was reformatted from single quotes to double quotes, creating a noisy diff. This makes it hard to see the actual functional change (adding ). Please revert the quote-style changes to match the existing file style, or split the formatting into a separate commit.\n\nOther minor notes:\n- Consider adding a timeout on the call for large exports.\n- The mutation pattern in tests works but is slightly fragile if tests ever run in parallel.\n\nPlease fix the quote churn in and this will be good to go.

[RolfKoenders]

Fixed in 6b87383.

Root cause: the CLI project had no .prettierrc, so the pre-commit hook reformatted src/index.ts to prettier's default (double quotes) even though the existing codebase uses single quotes. Added .prettierrc matching the project standard (singleQuote: true, same as app-backend). After reformatting, index.ts now only differs from main by the two functional lines: the registerExportCommand import and the register call.