Wire Astro content collections to the shared content/ directory

Adds a custom Astro loader that reads the Zola-style TOML frontmatter
(+++ ... +++) directly, so content/ stays the single source of truth
with no YAML conversion step. Defines writings/portfolio/bookshelf/
blogs collections and basic list/detail pages for each, rendering the
seed entries end-to-end (verified in-browser via `pnpm --filter site
dev`). This is the first runnable MVP: home, writings list + post
detail, portfolio, bookshelf (books and papers), and curated blogs
all render from real content/ files.

pnpm-lock.yaml

@@ -69,6 +69,12 @@ importers:
       astro:
         specifier: ^7.2.9
         version: 7.2.9(@emnapi/[email protected])(@emnapi/[email protected])(@types/[email protected])([email protected])([email protected])
+      marked:
+        specifier: ^18.0.11
+        version: 18.0.11
+      smol-toml:
+        specifier: ^1.8.0
+        version: 1.8.0
 
 packages:
 
@@ -5240,6 +5246,11 @@ packages:
     resolution: {integrity: sha512-4Ej49aYTDFIQ+uBkfX8GBvJGccoARxxPep+7aWTs55ozbjQJpW9M26Fe53vnGgvLeVzva/amzjQQaQu9w0vMhA==}
     hasBin: true
 
+  [email protected]:
+    resolution: {integrity: sha512-HnslJfsZkRPBDJRHvVtAaWlZHEpSu7u8LgQuJCELjRKuWR+hpq4A7sLq3p8HaI9ypVoXDXxV34CsQJEe1+J5Aw==}
+    engines: {node: '>= 20'}
+    hasBin: true
+
   [email protected]:
     resolution: {integrity: sha512-jfZW7cWS5y/1xswZo8VBOdudUiSd9nifYRWphc9M5D/ee4w4AoXLgBEdRbgVaxbMuagBPeUC5y2Hi8DO6o9aDg==}
 
@@ -13192,7 +13203,7 @@ snapshots:
       lodash.isstring: 4.0.1
       lodash.once: 4.1.1
       ms: 2.1.3
-      semver: 7.7.4
+      semver: 7.8.5
 
   [email protected]:
     dependencies:
@@ -13581,6 +13592,8 @@ snapshots:
       punycode.js: 2.3.1
       uc.micro: 2.1.0
 
+  [email protected]: {}
+
   [email protected]:
     dependencies:
       '@babel/runtime': 7.29.7