feat(posts): search, upcoming events, RSS feed

- Client-side search on /posts/ (full archive, ~2-char threshold)
- Upcoming-events block at top of /posts/ from isEvent+eventDate posts
- RSS feed at /posts/rss.xml via @astrojs/rss
- Layout head: rss autodiscovery link
- RSS subscribe link below the listing
- Style tweaks on QuoteBlock and PostOverviewBlock

yarn.lock

@@ -66,6 +66,15 @@
   dependencies:
     prismjs "^1.30.0"
 
+"@astrojs/rss@^4.0.18":
+  version "4.0.18"
+  resolved "https://registry.yarnpkg.com/@astrojs/rss/-/rss-4.0.18.tgz#9ce80003be5668545418d7e6ad53fe00e7a94d16"
+  integrity sha512-wc5DwKlbTEdgVAWnHy8krFTeQ42t1v/DJqeq5HtulYK3FYHE4krtRGjoyhS3eXXgfdV6Raoz2RU3wrMTFAitRg==
+  dependencies:
+    fast-xml-parser "^5.5.7"
+    piccolore "^0.1.3"
+    zod "^4.3.6"
+
 "@astrojs/sitemap@^3.7.2":
   version "3.7.2"
   resolved "https://registry.yarnpkg.com/@astrojs/sitemap/-/sitemap-3.7.2.tgz#6647a3f42f75435970abf72d456e1e9d8360dcdc"
@@ -2484,6 +2493,22 @@ fast-uri@^3.0.1:
   resolved "https://registry.yarnpkg.com/fast-uri/-/fast-uri-3.1.0.tgz#66eecff6c764c0df9b762e62ca7edcfb53b4edfa"
   integrity sha512-iPeeDKJSWf4IEOasVVrknXpaBV0IApz/gp7S2bb7Z4Lljbl2MGJRqInZiUrQwV16cpzw/D3S5j5Julj/gT52AA==
 
+fast-xml-builder@^1.1.4:
+  version "1.1.4"
+  resolved "https://registry.yarnpkg.com/fast-xml-builder/-/fast-xml-builder-1.1.4.tgz#0c407a1d9d5996336c0cd76f7ff785cac6413017"
+  integrity sha512-f2jhpN4Eccy0/Uz9csxh3Nu6q4ErKxf0XIsasomfOihuSUa3/xw6w8dnOtCDgEItQFJG8KyXPzQXzcODDrrbOg==
+  dependencies:
+    path-expression-matcher "^1.1.3"
+
+fast-xml-parser@^5.5.7:
+  version "5.5.12"
+  resolved "https://registry.yarnpkg.com/fast-xml-parser/-/fast-xml-parser-5.5.12.tgz#6e50e5a5bbb03c1dc72a9268a9bfe677b1b623b2"
+  integrity sha512-nUR0q8PPfoA/svPM43Gup7vLOZWppaNrYgGmrVqrAVJa7cOH4hMG6FX9M4mQ8dZA1/ObGZHzES7Ed88hxEBSJg==
+  dependencies:
+    fast-xml-builder "^1.1.4"
+    path-expression-matcher "^1.5.0"
+    strnum "^2.2.3"
+
 faye-websocket@0.11.4:
   version "0.11.4"
   resolved "https://registry.yarnpkg.com/faye-websocket/-/faye-websocket-0.11.4.tgz#7f0d9275cfdd86a1c963dc8b65fcc451edcbb1da"
@@ -3657,6 +3682,11 @@ parse5@^7.0.0, parse5@^7.3.0:
   dependencies:
     entities "^6.0.0"
 
+path-expression-matcher@^1.1.3, path-expression-matcher@^1.5.0:
+  version "1.5.0"
+  resolved "https://registry.yarnpkg.com/path-expression-matcher/-/path-expression-matcher-1.5.0.tgz#3b98545dc88ffebb593e2d8458d0929da9275f4a"
+  integrity sha512-cbrerZV+6rvdQrrD+iGMcZFEiiSrbv9Tfdkvnusy6y0x0GKBXREFg/Y65GhIfm0tnLntThhzCnfKwp1WRjeCyQ==
+
 pathe@^2.0.1, pathe@^2.0.3:
   version "2.0.3"
   resolved "https://registry.yarnpkg.com/pathe/-/pathe-2.0.3.tgz#3ecbec55421685b70a9da872b2cff3e1cbed1716"
@@ -4177,6 +4207,11 @@ strip-indent@^3.0.0:
   dependencies:
     min-indent "^1.0.0"
 
+strnum@^2.2.3:
+  version "2.2.3"
+  resolved "https://registry.yarnpkg.com/strnum/-/strnum-2.2.3.tgz#0119fce02749a11bb126a4d686ac5dbdf6e57586"
+  integrity sha512-oKx6RUCuHfT3oyVjtnrmn19H1SiCqgJSg+54XqURKp5aCMbrXrhLjRN9TjuwMjiYstZ0MzDrHqkGZ5dFTKd+zg==
+
 supports-color@^10.2.2:
   version "10.2.2"
   resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-10.2.2.tgz#466c2978cc5cd0052d542a0b576461c2b802ebb4"