Add jot related command with TF-IDF similarity

[Intina47]

Motivation

• Provide a lightweight, local similarity feature to surface related notes so users can explore patterns in their single-file notebook.
• Offer a simple CLI entry point to inspect related items from an existing note by ID.

Description

• Add a related subcommand to main and usage text for jot related <note-id> in the README via README.md changes.
• Implement note loading and preprocessing with loadNotes and extractNoteText to read ~/.jot/journal.txt into numbered notes.
• Add a small TF-IDF pipeline (tfidfVectors, tokenize, vectorNorm) and cosine similarity (cosineSimilarity) to compute note-to-note similarity and return the top 5 matches in jotRelated.
• Wire everything together so jotRelated prints matching note IDs and their raw lines, and validate input ranges with clear errors.

Testing

• Added tests TestJotRelatedOutputsTopMatches and TestJotRelatedRejectsOutOfRangeID in main_test.go.
• Ran go test ./... and the test suite passed (ok).
• Existing tests around jotInit, ensureJournal, and jotList were left intact and continued to succeed.

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Codex Task