Add jot link command to attach external issue/PR URLs to notes

[Intina47]

Motivation

• Provide a simple way to attach external issue/PR URLs to the most recent note so context can be preserved with a note.
• Persist URL metadata alongside the journal so links can be surfaced when reviewing notes.

Description

• Add a jot link <url> command entrypoint in main.go and implement jotLink to parse, enrich, and persist link metadata in ~/.jot/links.jsonl using a new LinkMetadata struct.
• Implement parseLinkURL to validate schemes and extract GitHub owner/repo/kind/number when applicable, and latestNoteTimestamp to associate links with the most recent note.
• Load stored links in jot list via loadLinksByTimestamp and render associated URLs under their linked note in the interactive listing.
• Add unit tests for URL parsing and storage (TestParseLinkURLGitHubPull, TestParseLinkURLRejectsScheme, TestJotLinkStoresMetadata) and update README.md with a usage example and storage location (~/.jot/links.jsonl).

Testing

• Ran the test suite with go test ./..., and all tests passed.
• Added unit tests exercise parsing and end-to-end storage of a GitHub PR URL, and those tests succeeded under CI-local run.
• Formatted changes with gofmt before running the tests.

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Use unique note IDs when storing links

Because jotLink persists only the note timestamp, links are keyed solely by the minute-level stamp used in note lines (format 2006-01-02 15:04 in jotInit). If a user records two notes within the same minute, they share the same NoteTimestamp, so a later jot link will show under all notes with that timestamp rather than just the most recent one. This violates the “attach to the most recent note” behavior and will surface incorrect associations whenever multiple notes exist in the same minute; consider storing a unique identifier (e.g., full line or line index) to disambiguate.

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