feat: UX & notification improvements — icons, events, chat names, link validation, templates

- Show entity icons on all cards with fallback defaults (providers, trackers, targets, bots)
- Enrich EventLog with provider_name, tracker_name, assets_count; add DB migration
- Dashboard events: filtering (type, provider, search), sorting, pagination, dynamic page size
- Friendly chat names on telegram target cards (resolve from TelegramChat table)
- Test message button on bot chat items with locale-aware messages
- Album public link validation on tracker save with auto-create dialog
- Support albums without public links: conditional <a href> in templates
- Fetch shared links during poll, enrich events with public_url/protected_url
- Per-asset public_url in template context ({share_url}/photos/{asset_id})
- Common date/location detection: common_date + common_location context vars
- Dual date formats: date_format (datetime) + date_only_format (date only)
- Template clone button, HTML link rendering in template preview
- Fix Telegram asset download 401: pass x-api-key headers through client
- Fix provider external_url matching for API key scoping
- Fix event timestamp timezone (append Z suffix for UTC)
- Localize event filter controls, test messages (EN/RU)
- Template variable UI helpers updated with all new fields
- CLAUDE.md: template system sync rules documentation

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

CLAUDE.md

@@ -52,3 +52,12 @@ NotificationTarget → template_config_id, type: "telegram"/"webhook", config: J
 - `user_id=0` on TemplateConfig = system default (EN/RU seeded on first startup)
 - DB: SQLite + async SQLAlchemy via sqlmodel, auto-created on startup
 - API: All CRUD routes under `/api/`, auth via JWT Bearer, `NOTIFY_BRIDGE_` env prefix
+
+## Template System Sync Rules
+
+**IMPORTANT**: When adding or changing template context variables, you MUST update ALL of these in sync:
+1. **`packages/core/.../templates/context.py`** — `build_template_context()` where variables are computed
+2. **`packages/server/.../api/template_configs.py`** — `_SAMPLE_CONTEXT` dict (for preview rendering)
+3. **`packages/server/.../api/template_configs.py`** — `get_template_variables()` endpoint (`event_vars`, `asset_fields`, `album_fields`, `scheduled_vars`, per-slot variable dicts)
+4. **`packages/core/.../templates/defaults/{en,ru}/*.jinja2`** — default template files using the new variables
+5. **`packages/core/.../providers/immich/provider.py`** — `IMMICH_VARIABLES` list (provider-specific variable definitions)