feat: date-range picker on the station history panel; drop PostgreSQL naming

/measurements/history/{code} accepts optional start/end date params that
override the hours window (end date inclusive). The dashboard history
card gains from/to date inputs beside the quick-range dropdown —
explicit dates win, changing the dropdown clears them. All user-facing
'PostgreSQL history' labels renamed to 'Station history'.

src/web_api.py

@@ -8,7 +8,7 @@ import os
 import secrets
 import time
 from contextlib import asynccontextmanager
-from datetime import datetime, timedelta
+from datetime import date, datetime, timedelta
 from decimal import Decimal
 from threading import Lock
 from typing import Any, Dict, List, Optional
@@ -609,9 +609,11 @@ async def get_postgres_history(
     station_code: str,
     hours: int = Query(168, ge=1),
     limit: int = Query(50000, ge=1, le=100000),
+    start: Optional[date] = Query(None, description="First day (overrides hours)"),
+    end: Optional[date] = Query(None, description="Last day, inclusive"),
 ):
     """Get historical measurements for a station from the configured database."""
-    cache_key = f"{station_code}:{hours}:{limit}"
+    cache_key = f"{station_code}:{hours}:{limit}:{start}:{end}"
     now = time.monotonic()
     with HISTORY_CACHE_LOCK:
         cached = HISTORY_CACHE.get(cache_key)
@@ -619,13 +621,20 @@ async def get_postgres_history(
             return cached[1]
     try:
         db_config = Config.get_database_config()
-        end_time = datetime.now()
+        end_time = (
+            datetime.combine(end, datetime.max.time()) if end else datetime.now()
+        )
+        start_time = (
+            datetime.combine(start, datetime.min.time())
+            if start
+            else end_time - timedelta(hours=hours)
+        )
         if db_config["type"] == "postgresql":
             history = PostgresHistory(db_config["connection_string"])
             data = await asyncio.to_thread(
                 history.station_history,
                 station_code,
-                end_time - timedelta(hours=hours),
+                start_time,
                 end_time,
                 limit,
             )
@@ -635,7 +644,7 @@ async def get_postgres_history(
                 raise RuntimeError("Database not available")
             rows = await asyncio.to_thread(
                 scraper.db_adapter.get_measurements_by_timerange,
-                end_time - timedelta(hours=hours),
+                start_time,
                 end_time,
                 [station_code],
             )