refactor: comprehensive codebase review — security, performance, quality, UX

Security:
- Fix NUT protocol command injection (validate names against safe regex)
- Enable Jinja2 autoescape=True to prevent HTML injection via external data
- Add WebhookProviderConfig validation model

Performance:
- Shared aiohttp.ClientSession singleton (replaces 40+ per-request sessions)
- Fix 4 N+1 queries with batch IN loads (poller, scheduler, memory, broadcast)
- asyncio.gather for Gitea commands and notification dispatcher
- Add DB indexes on NotificationTrackerState.tracker_id, CommandTrackerListener
- LRU cache for compiled Jinja2 templates
- Daily EventLog cleanup job (90-day retention)
- 30s HTTP timeout on all external calls
- GROUP BY for target type counts (replaces 7 sequential queries)

Code quality:
- Extract get_owned_entity() helper (replaces 11 duplicate functions)
- Extract slot_helpers.py (load_slots, save_slots, render_template_preview)
- Extract command_utils.py (tracker lookup, last event, collection IDs)
- Extract http_session.py (shared session lifecycle)
- Provider connection validation dedup (3x → 1 helper)
- Command dispatch tables replacing if/elif chains
- Album+links fetch helper (fetch_albums_with_links)
- Provider dispatch polymorphism (list_provider_collections)
- Immutable _enrich_assets (no longer mutates in-place)
- Fix _format_assets return type + handler unpacking

Frontend:
- Fix 18+ hardcoded English strings → t() with new i18n keys (en + ru)
- Mobile "More" nav panel with provider filter and search
- Shared Button.svelte component (4 variants, 2 sizes)
- Shared ErrorBanner.svelte component (8 pages updated)
- SvelteKit goto() replacing window.location.href
- Dashboard grid fixed for 4 cards, paginator opacity consistency

Functionality:
- max_instances=1 on scheduler jobs (prevents duplicate events)
- Webhook provider in watcher (prevents error spam)
- Fix stale SQLModel reference in poller
- Gitea get_repo() direct API call

packages/server/src/notify_bridge_server/services/action_runner.py

@@ -6,7 +6,6 @@ import logging
 from datetime import datetime, timezone
 from typing import Any
 
-import aiohttp
 from sqlmodel import select
 from sqlmodel.ext.asyncio.session import AsyncSession
 
@@ -159,27 +158,28 @@ async def _execute_with_provider(
         )
         from notify_bridge_core.providers.immich.client import ImmichClient
 
-        async with aiohttp.ClientSession() as http_session:
-            client = ImmichClient(
-                http_session,
-                provider_config.get("url", ""),
-                provider_config.get("api_key", ""),
+        from .http_session import get_http_session
+        http_session = await get_http_session()
+        client = ImmichClient(
+            http_session,
+            provider_config.get("url", ""),
+            provider_config.get("api_key", ""),
+        )
+        external_domain = provider_config.get("external_domain")
+        if external_domain:
+            client.external_domain = external_domain
+
+        # Verify connectivity
+        if not await client.ping():
+            return ActionResult(
+                success=False,
+                error=f"Cannot connect to Immich server ({provider_name})",
             )
-            external_domain = provider_config.get("external_domain")
-            if external_domain:
-                client.external_domain = external_domain
 
-            # Verify connectivity
-            if not await client.ping():
-                return ActionResult(
-                    success=False,
-                    error=f"Cannot connect to Immich server ({provider_name})",
-                )
-
-            executor = ImmichActionExecutor(client)
-            if dry_run:
-                return await executor.dry_run(action_type, rule_configs, action_config)
-            return await executor.execute(action_type, rule_configs, action_config)
+        executor = ImmichActionExecutor(client)
+        if dry_run:
+            return await executor.dry_run(action_type, rule_configs, action_config)
+        return await executor.execute(action_type, rule_configs, action_config)
 
     return ActionResult(
         success=False,