fix(ssr): apply theme CSS vars during SSR and enable client hydration

- ThemeService: remove isPlatformBrowser guard so CSS custom properties
  are applied during SSR/prerender — server-rendered HTML now carries the
  correct color scheme and gradients (fixes missing colors on test site).

- main.ts: add provideClientHydration() so Angular preserves the server-
  rendered DOM on the client instead of destroying and rebuilding it
  (fixes jarring full-page reload between static and dynamic versions).

- Tests: update theme.service.spec.ts to match new behaviour, expand
  coverage with gradient tests and empty-value handling (9 tests).
  Fix structured-data.component.spec.ts import paths. All 54 tests pass.

src/app/services/theme.service.spec.ts

@@ -0,0 +1,170 @@
+// Load the JIT compiler BEFORE any Angular router/common imports
+import '@angular/compiler';
+
+import { describe, it, expect, beforeEach, vi, afterEach } from 'vitest';
+import { Injector } from '@angular/core';
+import { ThemeService } from './theme.service';
+import { StationConfig } from '../interfaces/station-config';
+
+describe('ThemeService', () => {
+  let service: ThemeService;
+
+  const mockConfig: StationConfig = {
+    id: 1,
+    key: 'default',
+    callsign: 'KMOF',
+    name_primary: 'KMountain',
+    name_secondary: 'Flower Radio',
+    tagline: 'Community Radio',
+    frequency: '91.7',
+    founded_year: 2020,
+    nonprofit_type: '501c3',
+    ein: '12-3456789',
+    logo_url: 'https://kmtnflower.org/logo.png',
+    hero_background_url: '',
+    hero_icon_url: '',
+    hero_divider_url: '',
+    address: '',
+    phone: '',
+    email: 'info@kmtnflower.org',
+    website: 'kmtnflower.org',
+    donation_url: '',
+    stream_url: '',
+    stream_metadata_url: '',
+    play_store_icon_url: '',
+    play_store_url: '',
+    app_store_embed_html: '',
+    social_facebook: '',
+    social_twitter: '',
+    social_instagram: '',
+    social_youtube: '',
+    hero_subtitle: 'Your community-powered radio station.',
+    about_intro: 'About KMountain Flower Radio.',
+    about_donation_text: '',
+    schedule_intro: 'Our weekly schedule.',
+    events_intro: 'Community events.',
+    color_primary: '#4a90d9',
+    color_primary_light: '#6ba3eb',
+    color_primary_dark: '#2e6faa',
+    color_primary_muted: '#7baee7',
+    color_accent: '#e85d3a',
+    color_accent_light: '#eb7d5e',
+    color_accent_dark: '#c94422',
+    color_accent_muted: '#e98a72',
+    color_background: '#faf6f0',
+    color_text: '#333333',
+    color_success: '#4caf50',
+    color_danger: '#f44336',
+    color_info: '#2196f3',
+    color_white: '#ffffff',
+    color_light: '#eeeeee',
+    color_medium: '#9e9e9e',
+    color_black: '#000000',
+  } as const as StationConfig;
+
+  beforeEach(() => {
+    const injector = Injector.create({
+      providers: [ThemeService],
+    });
+    service = injector.get(ThemeService);
+  });
+
+  afterEach(() => {
+    // Clear all inline CSS custom properties after each test.
+    const root = document.documentElement.style;
+    for (const { prop } of [
+      { prop: '--color-primary' },
+      { prop: '--color-primary-light' },
+      { prop: '--color-primary-dark' },
+      { prop: '--color-primary-muted' },
+      { prop: '--color-accent' },
+      { prop: '--color-accent-light' },
+      { prop: '--color-accent-dark' },
+      { prop: '--color-accent-muted' },
+      { prop: '--color-cream' },
+      { prop: '--color-dark' },
+      { prop: '--color-success' },
+      { prop: '--color-danger' },
+      { prop: '--color-info' },
+      { prop: '--color-white' },
+      { prop: '--color-light' },
+      { prop: '--color-medium' },
+      { prop: '--color-black' },
+      { prop: '--sky-gradient' },
+      { prop: '--sunset-gradient' },
+      { prop: '--mixed-gradient' },
+    ]) {
+      root.removeProperty(prop);
+    }
+  });
+
+  it('should apply all CSS color variables', () => {
+    const setPropertySpy = vi.spyOn(document.documentElement.style, 'setProperty');
+    service.apply(mockConfig);
+    // 17 color fields + 3 gradient fields = 20 setProperty calls
+    expect(setPropertySpy).toHaveBeenCalledTimes(20);
+  });
+
+  it('should set primary color CSS variable', () => {
+    service.apply(mockConfig);
+    const rootStyle = document.documentElement.style;
+    expect(rootStyle.getPropertyValue('--color-primary')).toBe('#4a90d9');
+  });
+
+  it('should set accent color CSS variable', () => {
+    service.apply(mockConfig);
+    const rootStyle = document.documentElement.style;
+    expect(rootStyle.getPropertyValue('--color-accent')).toBe('#e85d3a');
+  });
+
+  it('should set background color to --color-cream', () => {
+    service.apply(mockConfig);
+    const rootStyle = document.documentElement.style;
+    expect(rootStyle.getPropertyValue('--color-cream')).toBe('#faf6f0');
+  });
+
+  it('should derive --sky-gradient from primary colors', () => {
+    service.apply(mockConfig);
+    const rootStyle = document.documentElement.style;
+    const sky = rootStyle.getPropertyValue('--sky-gradient');
+    expect(sky).toContain('linear-gradient(135deg');
+    expect(sky).toContain('#2e6faa');
+    expect(sky).toContain('#4a90d9');
+    expect(sky).toContain('#6ba3eb');
+  });
+
+  it('should derive --sunset-gradient from accent colors', () => {
+    service.apply(mockConfig);
+    const rootStyle = document.documentElement.style;
+    const sunset = rootStyle.getPropertyValue('--sunset-gradient');
+    expect(sunset).toContain('linear-gradient(135deg');
+    expect(sunset).toContain('#c94422');
+    expect(sunset).toContain('#e85d3a');
+    expect(sunset).toContain('#eb7d5e');
+  });
+
+  it('should derive --mixed-gradient from primary and accent', () => {
+    service.apply(mockConfig);
+    const rootStyle = document.documentElement.style;
+    const mixed = rootStyle.getPropertyValue('--mixed-gradient');
+    expect(mixed).toContain('linear-gradient(135deg');
+    expect(mixed).toContain('#2e6faa');
+    expect(mixed).toContain('#4a90d9');
+    expect(mixed).toContain('#e85d3a');
+  });
+
+  it('should work on both browser and server platforms (no platform check)', () => {
+    // ThemeService no longer guards on isPlatformBrowser — it applies CSS vars
+    // during SSR so the server-rendered HTML carries the correct theme.
+    service.apply(mockConfig);
+    const rootStyle = document.documentElement.style;
+    expect(rootStyle.getPropertyValue('--color-primary')).toBe('#4a90d9');
+  });
+
+  it('should skip fields with empty string values', () => {
+    const emptyConfig = { ...mockConfig, color_primary: '' } as StationConfig;
+    const setPropertySpy = vi.spyOn(document.documentElement.style, 'setProperty');
+    service.apply(emptyConfig);
+    expect(setPropertySpy).not.toHaveBeenCalledWith('--color-primary', '');
+  });
+});