feat: init Astro blog with wikilinks, KaTeX and local search

- Astro 5 static blog, zero runtime JS
- Obsidian wikilink remark plugin (slug matches Astro content collection)
- KaTeX math rendering, local search, TOC, archives, tags
- 5 posts on math/physics/ML topics
- deploy scripts for nginx + certbot + rsync

tsconfig.json

@@ -0,0 +1,11 @@
+{
+  "extends": "astro/tsconfigs/strict",
+  "include": [".astro/types.d.ts", "**/*"],
+  "exclude": ["dist"],
+  "compilerOptions": {
+    "baseUrl": ".",
+    "paths": {
+      "@/*": ["src/*"]
+    }
+  }
+}