Add unit tests for Observable, Tier, and Direction types

[jc-macdonald]

Summary

Unit tests for the core value types in protocols.py: Tier, Direction, and Observable.

Closes #1

Changes

1. Fix pre-existing E501 in __init__.py

Module docstring exceeded 88-char line limit; split to multi-line.

2. Add uv.lock to .gitignore

uv.lock was tracked but should not be; added to .gitignore and removed from index.

3. Tests for Tier and Direction enums

• All members present (4 tiers, 2 directions)
• .value strings match expected identifiers
• Lookup by value (Tier("embedded")) returns the correct singleton
• Invalid values raise ValueError
• Enum identity (is) holds

4. Tests for Observable frozen dataclass

• Field access matches constructor args
• Frozen immutability — assignment raises AttributeError
• Structural equality (same fields → equal)
• Inequality on name, tier, or direction differences
• Hashable — usable in set and as dict key
• repr includes all field values
• Duplicate names with different tiers are distinct objects

Stats

• 19 new tests in tests/test_protocols.py
• Coverage: 40% → 55.73%
• just ci passes (format, lint, mypy strict, coverage)