Cover project with tests

[petros]

Test Implementation Summary

Tests Added: 73 total

Module	Tests	Coverage
data.rs	40	Session, Label, Store + edge cases
storage.rs	13	Load, save, roundtrip, paths
commands.rs	20	add, list, remove, describe, config, resume

By Category:

1. Data Model Tests (26 unit + 14 edge cases)

• Session creation, serialization, description handling
• Label creation, add/remove sessions, latest_session
• Store CRUD operations
• Serialization roundtrips

2. Storage Tests (13)

• Load: missing file, empty file, whitespace, valid JSON, corrupt JSON
• Save: file creation, valid JSON output, overwrite
• Roundtrip: empty store, with data
• Path handling

3. Command Integration Tests (20)

• add: new label, append, description, current directory
• list: empty, all labels, specific label, nonexistent
• remove: entire label, specific session, error cases
• describe: set, update, clear, error cases
• resume: error conditions (can't test external command execution)
• config: basic functionality

4. Edge Cases (14)

• Empty session IDs and label names
• Unicode (Japanese, Russian, emoji) in all fields
• Very long session histories (1000 sessions)
• Many labels (100 with 10 sessions each)
• Special characters in descriptions and labels
• Duplicate session IDs handling
• Whitespace preservation