Adds detail enhancement for downstream tooling to consume full note

[polymorcodeus]

Summary

Adds a --full flag to todo detail that returns the complete companion-note body in a single call, removing the need for callers to reconstruct the note path and read the file themselves. Completes the detail enhancement for downstream tooling that consumes full note content.

What's new

• todo detail --full - Prints the entire companion-note body in human output instead of the 20-line preview.
• todo detail --json --full - Emits the full note text in a new note_body field.
• Internal API support - DetailOptions now carries a Full boolean and DetailResult carries a NoteBody string.

Usage

Command	Purpose
todo detail --full TSK-001	Show the complete note body
todo detail --json --full TSK-001	Return task metadata plus the full note body in note_body
todo detail --lines 5 TSK-001	Preview first 5 lines (unchanged)

Behavior changes / guardrails

• --lines is ignored when --full is set.
• --no-note still wins: --full --no-note produces no note output.
• note_preview and note_preview_truncated are omitted from JSON output under --full.
• detail remains read-only; last_updated is never bumped.
• Symlinked notes are read transparently via the existing NotePath resolution.

Testing

• Added unit and CLI tests for full note body, preview truncation, no note, --no-note, symlinked notes, and read-only behavior.
• make check runs fmt, vet, lint, and tests; all green.