Fix [object Object] in Variables button + allow preview of system templates

- Escape {{ }} in Svelte template (use {'{{ }}'} string expression)
- Allow _get() to access system templates (user_id=0) for preview

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

frontend/src/routes/template-configs/+page.svelte

@@ -133,7 +133,7 @@
 								<label class="text-xs text-[var(--color-muted-foreground)]">{t(`templateConfig.${slot.label}`)}</label>
 								{#if varsRef[slot.key]}
 									<button type="button" onclick={() => showVarsFor = slot.key}
-										class="text-xs text-[var(--color-muted-foreground)] hover:underline">{{ }} Variables</button>
+										class="text-xs text-[var(--color-muted-foreground)] hover:underline">{'{{ }}'} Variables</button>
 								{/if}
 							</div>
 							{#if (slot.rows || 2) > 2}

packages/server/src/immich_watcher_server/api/template_configs.py

@@ -165,6 +165,6 @@ def _response(c: TemplateConfig) -> dict:
 
 async def _get(session: AsyncSession, config_id: int, user_id: int) -> TemplateConfig:
     config = await session.get(TemplateConfig, config_id)
-    if not config or config.user_id != user_id:
+    if not config or (config.user_id != user_id and config.user_id != 0):
         raise HTTPException(status_code=404, detail="Template config not found")
     return config