Task 1: Simplify Capability; extend BoundEntity

- Make href Optional[str] = None for pattern capabilities
- Remove observe field (v2 architecture observes all hrefs)
- Add rt_filter, match_fn, key_fn fields to Capability
- Add entities default value tuple[()] to Capability
- Add key_override field to BoundEntity
- Update _key() to use key_override when present
- Update _make_observe_paths() to observe all unique hrefs (OBSERVE as accelerator)
- Guard _build() to skip pattern capabilities (href is None)
- Add test_bound_entity_key_override_takes_precedence test
- Update test_capability_defaults to remove observe assertion

All 61 tests passing (60 existing + 1 new).

tests/test_capability.py

@@ -6,7 +6,6 @@ def test_capability_defaults():
     c = Capability(href='/kidslock/vs/0',
                    entities=(BinarySensorDesc(key='child_lock', field='x.com.samsung.da.kidsLock'),))
     assert c.poll_tier == 'warm'
-    assert c.observe is True
     assert c.active_when is None
     assert len(c.entities) == 1