feat(angular/directive): export FeatureFlagDirectiveContext (#1346)

## This PR
Exports `FeatureFlagDirectiveContext<T>` from the Angular SDK public
API.

This change enables external consumers (such as the OpenFeature CLI
Angular generator) to safely extend `FeatureFlagDirective<T>` while
preserving proper template typing.

Previously, `FeatureFlagDirectiveContext<T>` was not exported, which
made it impossible to correctly type:
`TemplateRef<FeatureFlagDirectiveContext<T>>` when extending
`FeatureFlagDirective<T>` outside of the SDK.

This PR:
- Exports `FeatureFlagDirectiveContext<T>` from the `angular-sdk` public
API
- Does not introduce any breaking changes
- Does not modify runtime behavior
- Only expands the public surface to support extension use cases

This change is required to support the CLI refactor that generates
derived structural directives instead of relying on `hostDirectives`.

### Related Issues
Fixes #1345 

### Notes
- This is a non-breaking change.
- No internal logic has been modified.
- The export simply makes an already existing type publicly available.

### Follow-up Tasks
- Update the OpenFeature CLI Angular generator to extend
`FeatureFlagDirective<T>` directly (instead of using `hostDirectives`)
see : open-feature/cli#217

### How to test
1. Build the Angular SDK package.
2. In an external Angular project, create a directive extending:
`FeatureFlagDirective<boolean>`
3. Inject: `TemplateRef<FeatureFlagDirectiveContext<boolean>>`
4. Verify:
   - TypeScript compiles without internal imports
   - Template typing is preserved
   - No runtime behavior changes occur

---------

Signed-off-by: backtrack5r3 <flennertom@gmail.com>

Author: tomflenner

packages/angular/projects/angular-sdk/src/lib/feature-flag.directive.spec.ts

@@ -7,6 +7,7 @@ import { TestingProvider } from '../test/test.utils';
 import { v4 } from 'uuid';
 import {
   BooleanFeatureFlagDirective,
+  FeatureFlagDirectiveContext,
   NumberFeatureFlagDirective,
   ObjectFeatureFlagDirective,
   StringFeatureFlagDirective,
@@ -181,6 +182,22 @@ class TestComponent {
   protected readonly JSON = JSON;
 }
 
+describe('FeatureFlagDirectiveContext', () => {
+  it('should initialize $implicit and evaluationDetails from EvaluationDetails', () => {
+    const mockDetails = {
+      value: true,
+      reason: 'STATIC',
+      flagKey: 'test-flag',
+      flagMetadata: {},
+    };
+
+    const context = new FeatureFlagDirectiveContext(mockDetails);
+
+    expect(context.$implicit).toBe(true);
+    expect(context.evaluationDetails).toEqual(mockDetails);
+  });
+});
+
 describe('FeatureFlagDirective', () => {
   describe('thenTemplate', () => {
     it('should not be rendered if disabled by the flag', async () => {

packages/angular/projects/angular-sdk/src/lib/feature-flag.directive.ts

@@ -21,7 +21,37 @@ import {
   OpenFeature,
 } from '@openfeature/web-sdk';
 
-class FeatureFlagDirectiveContext<T extends FlagValue> {
+/**
+ * Represents the template context provided by feature flag structural directives
+ * (`*booleanFeatureFlag`, `*numberFeatureFlag`, `*stringFeatureFlag`, `*objectFeatureFlag`).
+ *
+ * This class defines the shape of the data available in your templates when using
+ * feature flag directives. It exposes:
+ * - **`$implicit`** — The evaluated flag value, bound via `let value` in templates.
+ * - **`evaluationDetails`** — The full {@link EvaluationDetails} object containing
+ *   metadata such as `flagKey`, `reason`, `variant`, `flagMetadata`, and potential error info.
+ *
+ * @usageNotes
+ *
+ * If you need to reference a feature flag template programmatically (e.g. with `@ViewChild`),
+ * use this class as the generic parameter:
+ *
+ * ```typescript
+ * @ViewChild('flagTpl')
+ * flagTpl!: TemplateRef<FeatureFlagDirectiveContext<boolean>>;
+ * ```
+ *
+ * This is also useful when building custom components or wrappers that accept
+ * feature flag templates as inputs:
+ *
+ * ```typescript
+ * @Input() customTemplate: TemplateRef<FeatureFlagDirectiveContext<string>>;
+ * ```
+ *
+ * @template T The type of the flag value (`boolean`, `number`, `string`, or `JsonValue`).
+ *
+ */
+export class FeatureFlagDirectiveContext<T extends FlagValue> {
   $implicit!: T;
   evaluationDetails: EvaluationDetails<T>;