feat: add Web Clipper intake protocol (openknowledge://clip) and clip-intake schema (#1174)

[Adityakk9031]

Resolves #1174

Description

This PR introduces the secure Web Clipper Desktop Intake Protocol (openknowledge://clip) and openknowledge.clip/v1 envelope schema as proposed in #1174.

What Changed

• Core Package (packages/core):
  • Added ClipPayloadSchema and OkClipPayload in packages/core/src/schemas/api/clip-intake.ts validating openknowledge.clip/v1 Markdown envelopes.
  • Re-exported ClipPayloadSchema in core API schemas.
• Desktop Package (packages/desktop):
  • Added parseClipUrl in packages/desktop/src/main/url-scheme.ts to parse and validate openknowledge://clip?destination=<id>&clipboard=true deep links with path traversal and null-byte defenses.
  • Created packages/desktop/src/main/clip-intake.ts providing filename sanitization and "Keep both" collision resolution (article.md -> article-1.md).
• Tests & Changeset:
  • Added comprehensive unit tests in packages/desktop/src/main/url-scheme-clip.test.ts (9/9 tests passing).
  • Included changeset .changeset/add-web-clipper-intake-protocol.md.

Testing

• Ran npx vitest run src/main/url-scheme-clip.test.ts (all 9 unit tests passed).
• Verified parseClipUrl rejects null-bytes, missing destinations, invalid hosts, and path traversal attempts.

[github-actions]

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[Adityakk9031]

@tim-inkeep and @anubra266 have a look