Add database overview feature with metrics and UI enhancements

This commit introduces a detailed database overview endpoint and service, providing key metrics such as replication status, database sizes, and performance indicators. On the frontend, a new UI section displays these metrics along with improved forms and troubleshooting tips. Enhancements improve user experience by adding informative tooltips and formatting for byte and time values.

backend/app/services/overview_service.py

@@ -0,0 +1,46 @@
+import asyncio
+import time
+import asyncpg
+from app.models.models import Target
+from app.schemas.overview import DatabaseOverviewOut
+from app.services.collector import build_target_dsn
+from app.services.infra_probe import get_disk_space_provider
+from app.services.overview_collector import collect_overview
+
+_CACHE_TTL_SECONDS = 20
+_cache: dict[int, tuple[float, DatabaseOverviewOut]] = {}
+_locks: dict[int, asyncio.Lock] = {}
+
+
+def _get_lock(target_id: int) -> asyncio.Lock:
+    if target_id not in _locks:
+        _locks[target_id] = asyncio.Lock()
+    return _locks[target_id]
+
+
+async def get_target_overview(target: Target) -> DatabaseOverviewOut:
+    now = time.time()
+    cached = _cache.get(target.id)
+    if cached and (now - cached[0]) < _CACHE_TTL_SECONDS:
+        return cached[1]
+
+    lock = _get_lock(target.id)
+    async with lock:
+        cached = _cache.get(target.id)
+        now = time.time()
+        if cached and (now - cached[0]) < _CACHE_TTL_SECONDS:
+            return cached[1]
+
+        conn = await asyncpg.connect(dsn=build_target_dsn(target))
+        try:
+            payload = await collect_overview(
+                conn=conn,
+                disk_provider=get_disk_space_provider(),
+                target_host=target.host,
+                cache_ttl_seconds=_CACHE_TTL_SECONDS,
+            )
+        finally:
+            await conn.close()
+
+        _cache[target.id] = (time.time(), payload)
+        return payload