feat(v0.6-3a): adapter_config foundation -- migration + defaults registry + typed accessor

Closes the foundation slice of audit doc Section A (Rule 17). Lands two
SQLite tables, the seed routine that populates them from a Python
defaults registry, and a typed accessor that handler code will read in
v0.6-3b. No handler changes in this commit -- ZERO behavior risk, every
existing test still passes (721 / 69 skipped / 0 failed).

v6.sql tables:
  - adapter_config(adapter, key, value_json, default_json, type, description,
                    updated_at) PRIMARY KEY(adapter, key) -- JSON-encoded
                    values flow through a single column uniformly. CHECK
                    constraint on `type` closes the vocab (int/float/str/
                    bool/json).
  - adapter_meta(adapter PK, display_name, include_in_llm_context,
                  description, updated_at) -- per-adapter metadata + the
                  user-scopable LLM-context toggle (Matt refinement #5).

meshai/adapter_config/ package:
  - defaults.py: REGISTRY dict mapping (adapter, key) -> {default, type,
    description}. Covers audit doc sections A.1-A.12: wfigs, nws,
    usgs_quake, swpc, usgs_nwis, incident family (tomtom_incidents,
    state_511_atis, itd_511, shared "incident"), central consumer,
    dispatcher, band_conditions, geocoder, firms, pipeline (Inhibitor +
    Grouper). ~85 keys total. ADAPTER_META covers 15 adapters with
    display_name + include_in_llm_context defaulting to True. Per Matt
    refinement #3, every default matches the current handler constant
    EXACTLY -- first deploy behavior is unchanged.
  - _accessor.py: AdapterConfig class with `adapter_config.<adapter>.<key>`
    syntax. Read pipeline: in-memory cache hit -> SQL -> registry
    fallback (with WARNING) -> AttributeError. Process-wide cache; PUT
    via v0.6-3c REST API calls invalidate_cache() to drop the cache.
    GIL-atomic dict reads on the fast path (handlers call this hot).
  - __init__.py: seed_defaults(conn) -- INSERT OR IGNOREs one row per
    registry entry. Idempotent, never overwrites user edits.

Wiring:
  - meshai/persistence/db.py: SCHEMA_VERSION 5 -> 6, and init_db() now
    calls seed_defaults() after migrations apply.
  - meshai/main.py: _init_components() now calls init_db() FIRST (per
    commit #1 lessons-learned: a startup-time migration is required
    when handlers will rely on the new schema; lazy-on-first-handler
    is fine for v4/v5 but not for v6 where handler reads start in
    v0.6-3b).
  - tests/conftest.py: autouse fixture now calls init_db() + clears
    the accessor cache around each test, so every test gets the v6
    seed AND a clean cache without per-test boilerplate.

Tests (tests/test_adapter_config_foundation.py, 24 cases):
  - v6 tables exist + schema_meta at 6 + type-vocabulary CHECK enforced
  - seed populates every REGISTRY + ADAPTER_META row, value_json ==
    default_json on first seed, type matches
  - seed is idempotent + does not overwrite user edits
  - accessor returns correctly typed values for int/float/str/bool/
    json list/json dict/json None
  - cache hit: second read does not touch the DB (patched _load_from_db
    raises, accessor still succeeds)
  - invalidate_cache forces a re-read; mutated DB value wins
  - registry fallback path triggers when a row is missing (with WARNING)
  - unknown key raises AttributeError
  - setattr blocked (writes go via the REST API in 3c)
  - every default JSON round-trips cleanly; every type is in vocabulary
  - ADAPTER_META covers every adapter in REGISTRY

Test count: 697 -> 721 (+24 new, 0 regressions).

v0.6-3b will wire handlers one at a time (wfigs, nws, quake, swpc, nwis,
incident, central, dispatcher, band_conditions, geocoder, firms). Per
the audit lock, defaults match exactly so each wiring step is a pure
refactor -- bisect-safe.

v0.6-3c lands the /api/adapter-config CRUD + the AdapterConfig.tsx
dashboard editor + cache invalidation on PUT.

Refs audit doc v0.6-phase1-audit.md Section A + finding #4.

tests/conftest.py

@@ -21,11 +21,32 @@ from meshai.persistence import db as _persistence_db
 
 @pytest.fixture(autouse=True)
 def _isolate_meshai_db(tmp_path, monkeypatch):
-    """Point MESHAI_DB_PATH at a tmp file per test."""
+    """Point MESHAI_DB_PATH at a tmp file per test + run init_db so the
+    v6 adapter_config seed lands before any test code runs.
+
+    v0.6-3a: init_db() applies pending migrations AND seeds
+    adapter_config from the defaults registry. Tests that read via
+     need the seed in place.
+    """
     p = str(tmp_path / "meshai-test-isolated.sqlite")
     monkeypatch.setenv("MESHAI_DB_PATH", p)
     _persistence_db._initialised.clear()
     close_thread_connection()
+    # Clear the adapter_config accessor cache so the prior tests
+    # in-memory cache does not leak into this test.
+    try:
+        from meshai.adapter_config import invalidate_cache
+        invalidate_cache()
+    except Exception:
+        pass
+    # Eager init: applies v1..v6 migrations + seeds adapter_config.
+    from meshai.persistence import init_db
+    init_db()
     yield p
     close_thread_connection()
     _persistence_db._initialised.discard(p)
+    try:
+        from meshai.adapter_config import invalidate_cache
+        invalidate_cache()
+    except Exception:
+        pass