refactor(nws): remove internal AsyncLimiter rate limiting

The NWSAdapter had an internal AsyncLimiter that duplicated the
supervisor's rate-limit guarantee. When cadence changed, only
state.adapter.cadence_s was updated, not the internal limiter,
causing the cadence-decrease bug.

Since the supervisor already enforces rate limiting via
last_completed_poll + cadence_s scheduling, the adapter-level
limiter was redundant and caused the 30-second blocking observed
in diagnostic logs.

Removes:
- aiolimiter import
- self.cadence_s attribute (unused elsewhere)
- self._limiter creation
- async with self._limiter context in _fetch_alerts

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/central/adapters/nws.py

@@ -10,7 +10,6 @@ from pathlib import Path
 from typing import Any
 
 import aiohttp
-from aiolimiter import AsyncLimiter
 from tenacity import (
     retry,
     stop_after_attempt,
@@ -199,11 +198,9 @@ class NWSAdapter(SourceAdapter):
         cursor_db_path: Path,
     ) -> None:
         self.config = config
-        self.cadence_s = config.cadence_s
         self.states = set(s.upper() for s in config.states)
         self.cursor_db_path = cursor_db_path
         self._session: aiohttp.ClientSession | None = None
-        self._limiter = AsyncLimiter(1, config.cadence_s)
         self._db: sqlite3.Connection | None = None
 
     async def startup(self) -> None:
@@ -329,38 +326,37 @@ class NWSAdapter(SourceAdapter):
     )
     async def _fetch_alerts(self) -> tuple[int, dict[str, Any] | None, str | None]:
         """Fetch alerts from NWS API with conditional request."""
-        async with self._limiter:
-            if not self._session:
-                raise RuntimeError("Session not initialized")
+        if not self._session:
+            raise RuntimeError("Session not initialized")
 
-            headers: dict[str, str] = {}
-            cursor = self._get_cursor()
-            if cursor:
-                headers["If-Modified-Since"] = cursor
+        headers: dict[str, str] = {}
+        cursor = self._get_cursor()
+        if cursor:
+            headers["If-Modified-Since"] = cursor
 
-            async with self._session.get(NWS_API_URL, headers=headers) as resp:
-                if resp.status in (429, 403):
-                    retry_after = resp.headers.get("Retry-After", "60")
-                    try:
-                        wait_time = int(retry_after)
-                    except ValueError:
-                        wait_time = 60
-                    logger.warning(
-                        "Rate limited by NWS",
-                        extra={"status": resp.status, "retry_after": wait_time}
-                    )
-                    await asyncio.sleep(wait_time)
-                    raise aiohttp.ClientError(f"Rate limited: {resp.status}")
+        async with self._session.get(NWS_API_URL, headers=headers) as resp:
+            if resp.status in (429, 403):
+                retry_after = resp.headers.get("Retry-After", "60")
+                try:
+                    wait_time = int(retry_after)
+                except ValueError:
+                    wait_time = 60
+                logger.warning(
+                    "Rate limited by NWS",
+                    extra={"status": resp.status, "retry_after": wait_time}
+                )
+                await asyncio.sleep(wait_time)
+                raise aiohttp.ClientError(f"Rate limited: {resp.status}")
 
-                if resp.status == 304:
-                    return (304, None, None)
+            if resp.status == 304:
+                return (304, None, None)
 
-                resp.raise_for_status()
+            resp.raise_for_status()
 
-                data = await resp.json()
-                last_modified = resp.headers.get("Last-Modified")
+            data = await resp.json()
+            last_modified = resp.headers.get("Last-Modified")
 
-                return (resp.status, data, last_modified)
+            return (resp.status, data, last_modified)
 
     def _normalize_feature(self, feature: dict[str, Any]) -> Event | None:
         """Normalize a GeoJSON feature to an Event."""