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

public/sitemap.xml

@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <url>
+    <loc>https://kmountainflower.org/</loc>
+    <changefreq>daily</changefreq>
+    <priority>1.0</priority>
+  </url>
+  <url>
+    <loc>https://kmountainflower.org/about</loc>
+    <changefreq>weekly</changefreq>
+    <priority>0.8</priority>
+  </url>
+  <url>
+    <loc>https://kmountainflower.org/schedule</loc>
+    <changefreq>weekly</changefreq>
+    <priority>0.8</priority>
+  </url>
+  <url>
+    <loc>https://kmountainflower.org/events</loc>
+    <changefreq>daily</changefreq>
+    <priority>0.8</priority>
+  </url>
+  <url>
+    <loc>https://kmountainflower.org/contact</loc>
+    <changefreq>monthly</changefreq>
+    <priority>0.5</priority>
+  </url>
+</urlset>