perf(bundle): lazy-load the nunjucks template engine (#2535)

Closes #2531.

## Summary

The full `nunjucks` templating engine (~226KB) plus `ha-nunjucks`
(~46KB) — roughly **272KB, ~13% of the eager entry chunk** — was
statically imported and downloaded by every card on initial load, even
though templates only apply when a config value contains a `{{ … }}` /
`{% … %}` delimiter. Most cards use no templates and never need the
engine.

This defers the engine behind a dynamic `import('ha-nunjucks/dist')` so
it ships in a separate, on-demand chunk instead of the eager
`card-*.js`.

## Approach

The render path (`TemplateRenderer.renderRecursively`) is **kept
synchronous** — it is called from many synchronous hot paths
(condition/trigger evaluators, picture-elements rendering, actions,
folder matchers), and making it async would be a large, high-risk
refactor of the evaluation core.

Instead:

- **New `src/card-controller/templates/engine.ts`** — a module-level
singleton lazy loader (`loadTemplateEngine()` / `getTemplateEngine()`)
shared across all `TemplateRenderer` instances, plus a
`containsTemplate()` delimiter helper.
- **Delimiter gating** — strings without a delimiter never touch the
engine (the overwhelming majority of renders).
- **Pre-warm at config time** — because every template string originates
in the config, a new mandatory `TEMPLATE_ENGINE` initialization aspect
loads the engine before first render whenever the config contains a
delimiter. This **guarantees no raw `{{ … }}` flash**: content/condition
rendering is blocked until the engine is present for template-using
cards. Cards without templates never load it.

## Result

- nunjucks + ha-nunjucks move out of the eager chunk into a separate
chunk fetched only when a card actually uses templates.
- No change to the synchronous public render API; condition/trigger
evaluation core untouched.

## Tests

- New `engine.ts` loader coverage (concurrent load, cached reuse,
not-loaded fallback).
- The 11 existing test files that render real (delimiter-bearing)
templates declare their dependency explicitly via
`beforeAll(loadTemplateEngine)` — no global/implicit setup hook.
- Full suite green (4764 tests), lint and ts-prune clean, per-file 100%
coverage maintained for the affected directories.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_016ykWemdkZrgywvC71pHc6c

---
_Generated by [Claude
Code](https://claude.ai/code/session_016ykWemdkZrgywvC71pHc6c)_

tests/condition-trigger/triggers/triggers/numeric-state.test.ts

@@ -1,6 +1,10 @@
 import type { HassEntities, HassEntity } from 'home-assistant-js-websocket';
 import { afterEach, beforeEach, describe, expect, it, vi, type Mock } from 'vitest';
 
+import {
+  TemplateManager,
+  type TemplateRenderer,
+} from '../../../../src/card-controller/templates';
 import { ConditionStateManager } from '../../../../src/condition-trigger/conditions/state-manager';
 import { NumericStateTrigger } from '../../../../src/condition-trigger/triggers/triggers/numeric-state';
 import type { TriggerOfType } from '../../../../src/condition-trigger/triggers/triggers/types';
@@ -15,6 +19,7 @@ const THRESHOLD = 'input_number.limit';
 describe('NumericStateTrigger', () => {
   const create = (
     config: TriggerOfType<'numeric_state'>,
+    templateRenderer?: TemplateRenderer,
   ): {
     trigger: NumericStateTrigger;
     stateManager: ConditionStateManager;
@@ -24,7 +29,9 @@ describe('NumericStateTrigger', () => {
     const callback = vi.fn();
     const trigger = new NumericStateTrigger(
       config,
-      createTriggerEvaluatorContext({ stateManager }),
+      createTriggerEvaluatorContext(
+        templateRenderer ? { stateManager, templateRenderer } : { stateManager },
+      ),
     );
     return { trigger, stateManager, callback };
   };
@@ -154,13 +161,19 @@ describe('NumericStateTrigger', () => {
     expect(callback).toHaveBeenCalledTimes(1);
   });
 
-  it('should match the rendered value_template', () => {
-    const { trigger, stateManager, callback } = create({
-      trigger: 'numeric_state',
-      entity_id: SENSOR,
-      value_template: `{{ states('${SENSOR}') | float * 10 }}`,
-      above: 20,
-    });
+  it('should match the rendered value_template', async () => {
+    const templateManager = new TemplateManager();
+    await templateManager.loadRenderer();
+
+    const { trigger, stateManager, callback } = create(
+      {
+        trigger: 'numeric_state',
+        entity_id: SENSOR,
+        value_template: `{{ states('${SENSOR}') | float * 10 }}`,
+        above: 20,
+      },
+      templateManager,
+    );
     trigger.subscribe(callback);
 
     // Template value 1 * 10 = 10: arms.

tests/condition-trigger/triggers/triggers/template.test.ts

@@ -1,11 +1,26 @@
-import { afterEach, beforeEach, describe, expect, it, vi, type Mock } from 'vitest';
+import {
+  afterEach,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+  vi,
+  type Mock,
+} from 'vitest';
 
+import { TemplateManager } from '../../../../src/card-controller/templates';
 import { ConditionStateManager } from '../../../../src/condition-trigger/conditions/state-manager';
 import { TemplateTrigger } from '../../../../src/condition-trigger/triggers/triggers/template';
 import type { TriggerOfType } from '../../../../src/condition-trigger/triggers/triggers/types';
 import { createHASS, createStateEntity } from '../../../test-utils';
 import { createTriggerEvaluatorContext } from './test-utils';
 
+const templateManager = new TemplateManager();
+beforeAll(async () => {
+  await templateManager.loadRenderer();
+});
+
 const ENTITY_ONE = 'sensor.foo';
 const ENTITY_TWO = 'sensor.bar';
 
@@ -24,7 +39,7 @@ describe('TemplateTrigger', () => {
     const callback = vi.fn();
     const trigger = new TemplateTrigger(
       config,
-      createTriggerEvaluatorContext({ stateManager }),
+      createTriggerEvaluatorContext({ stateManager, templateRenderer: templateManager }),
     );
     return { trigger, stateManager, callback };
   };

tests/condition-trigger/triggers/triggers/test-utils.ts

@@ -1,13 +1,12 @@
-import { TemplateRenderer } from '../../../../src/card-controller/templates';
 import { ConditionStateManager } from '../../../../src/condition-trigger/conditions/state-manager';
 import type { TriggerEvaluatorContext } from '../../../../src/condition-trigger/triggers/triggers/types';
-import { createHASSManager } from '../../../test-utils';
+import { createHASSManager, createMockTemplateRenderer } from '../../../test-utils';
 
 export const createTriggerEvaluatorContext = (
   context?: Partial<TriggerEvaluatorContext>,
 ): TriggerEvaluatorContext => ({
   stateManager: new ConditionStateManager(),
-  templateRenderer: new TemplateRenderer(),
+  templateRenderer: createMockTemplateRenderer(),
   hassManager: createHASSManager(),
   ...context,
 });