fix(seo): comprehensive SEO improvements per expert audit

- Add public/robots.txt (allow all, disallow /admin and /login, reference sitemap)
- Add public/sitemap.xml (5 public routes with change frequencies and priorities)
- Fix heading hierarchy: h2 -> h1 on about, schedule, events, contact pages
- Remove dead footer href="#" links:
  - Volunteer/Corporate Giving/Planned Giving -> routerLink to /contact with subject query param
  - Social media links -> conditional on config().social_* fields (hidden when empty)
- Fix logo ARIA: add aria-hidden="true" to decorative logo in about page divider
- Add social_facebook, social_twitter, social_instagram, social_youtube to:
  - StationConfig DB model + startup migration
  - StationConfigResponse and StationConfigUpdate schemas
  - Frontend StationConfig TypeScript interface
- Fix events "Learn More" dead link -> routerLink to /contact

backend/app/schemas.py

@@ -78,6 +78,11 @@ class StationConfigResponse(BaseModel):
     play_store_icon_url: str
     play_store_url: str
     app_store_embed_html: str
+    # Social media
+    social_facebook: str
+    social_twitter: str
+    social_instagram: str
+    social_youtube: str
     # Page content
     hero_subtitle: str
     about_intro: str
@@ -129,6 +134,11 @@ class StationConfigUpdate(BaseModel):
     play_store_icon_url: Optional[str] = None
     play_store_url: Optional[str] = None
     app_store_embed_html: Optional[str] = None
+    # Social media
+    social_facebook: Optional[str] = None
+    social_twitter: Optional[str] = None
+    social_instagram: Optional[str] = None
+    social_youtube: Optional[str] = None
     # Page content
     hero_subtitle: Optional[str] = None
     about_intro: Optional[str] = None