docs: add Hugo partials structure documentation

AGENTS.md

@@ -0,0 +1,32 @@
+# Hugo Partials Structure
+
+This site uses the **hugo-coder** theme with the **hugo-cloak-email** plugin.
+
+## Partial Directories
+
+### `layouts/partials/`
+Standard Hugo partial override directory. Files here override theme partials when called via `partial "name.html"`.
+
+**Used for:**
+- `cloakemail.html` — Overrides hugo-cloak-email's default partial
+- `head.html` — Adds font preloading and AdSense
+- `footer.html` — Custom footer with `[commit]` placeholder
+- `home/social.html` — Integrates cloakemail for email obfuscation
+- `home/avatar.html` — Custom avatar rendering
+
+### `layouts/_partials/`
+Non-standard directory used by **hugo-coder** theme. Files here override theme partials when called via `partial "_partials/name.html"`.
+
+**Used for:**
+- `csp.html` — Custom Content Security Policy with additional script sources
+
+## How Hugo Resolves Partials
+
+Hugo's lookup order tries user overrides first, then falls back to theme files:
+
+1. `layouts/partials/` or `layouts/_partials/` (your overrides)
+2. `themes/<theme>/layouts/partials/` or `themes/<theme>/layouts/_partials/`
+
+## Verification
+
+Run `hugo --templateMetrics` to see which templates are actually being used and their execution counts.