feat(seo): Phase 2 — route-level metadata service and JSON-LD structured data

Add SeoService for dynamic metadata management:
- Per-route document titles (e.g., 'KMountain Flower Radio — About')
- Meta descriptions from station config per route
- Canonical URLs, Open Graph tags, Twitter Card tags
- Input sanitization (HTML stripping, URL validation, attribute escaping)
- noindex robots directives for /login and /admin routes
- Centralized router watcher (zero per-component boilerplate)

Add StructuredDataService + StructuredDataComponent for JSON-LD:
- Organization schema (NCBOrganization) site-wide with contact info
- WebSite schema with publisher info
- WebPage schema per-route with breadcrumbs
- Dynamic Event schema on /events page
- RadioSeason schema on /schedule page

Wire up SeoService.watchRouter() in app-root ngOnInit.
Wire up StructuredDataComponent in app-root template.
Wire up EventsComponent and ScheduleComponent to feed data to
StructuredDataService for dynamic schema injection.

Includes full test suite for SeoService (22 tests).

src/app/structured-data/structured-data.component.ts

@@ -0,0 +1,56 @@
+import { Component, effect, inject } from '@angular/core';
+import { StructuredDataService } from '../services/structured-data.service';
+
+/**
+ * Renders JSON-LD structured data as `<script type="application/ld+json">` tags
+ * in the document <head>.
+ *
+ * Reads from StructuredDataService.structuredData() and keeps the head tags
+ * in sync on every route change or config update.
+ *
+ * Tags are identified by the data attribute `data="structured-data"` so they
+ * can be cleaned up on destroy without affecting other <head> scripts.
+ */
+@Component({
+  selector: 'app-structured-data',
+  standalone: true,
+  template: '', // renders nothing in the body — writes to <head>
+})
+export class StructuredDataComponent {
+  private service = inject(StructuredDataService);
+
+  constructor() {
+    effect(() => {
+      const entries = this.service.structuredData();
+      this.renderEntries(entries);
+    });
+  }
+
+  ngOnDestroy(): void {
+    this.clearTags();
+  }
+
+  // ── Private ────────────────────────────────────────────────────
+
+  /** Write JSON-LD script tags to <head>, replacing any previous ones. */
+  private renderEntries(entries: unknown[]): void {
+    this.clearTags();
+
+    const head = document.head;
+    for (const entry of entries) {
+      const script = document.createElement('script');
+      script.type = 'application/ld+json';
+      script.setAttribute('data', 'structured-data');
+      script.textContent = JSON.stringify(entry);
+      head.appendChild(script);
+    }
+  }
+
+  /** Remove all previously injected structured-data script tags. */
+  private clearTags(): void {
+    const tags = document.querySelectorAll('script[data="structured-data"]');
+    for (const tag of tags) {
+      tag.remove();
+    }
+  }
+}