Fast-fail DB writes: 5s timeout, disable after first failure

Prevents broken Neon connections from blocking the entire pipeline
with thousands of timeout waits. After one failed write, DB is
disabled for the rest of the run and pipeline continues in-memory.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/pipeline.py

@@ -116,15 +116,16 @@ class HeatRiskPipeline:
     async def _db_write(self, fn, *args, **kwargs):
         """Call a database CRUD function. Silently skip if no db or on error.
 
-        Usage: await self._db_write(insert_daily_reading, self.db, {...})
-        The function is only called (and its coroutine created) when self.db is set.
+        Disables DB writes after first failure to avoid blocking the pipeline
+        with repeated connection timeouts.
         """
         if self.db is None:
             return None
         try:
-            return await fn(*args, **kwargs)
+            return await asyncio.wait_for(fn(*args, **kwargs), timeout=5.0)
         except Exception as exc:
-            logger.warning("Database write failed (non-fatal): %s", exc)
+            logger.warning("Database write failed, disabling DB for this run: %s", exc)
+            self.db = None  # Stop trying — don't block the pipeline
             return None
 
     async def run(self) -> PipelineRunResult: