Refactor and other improvements

CLAUDE.md

@@ -302,7 +302,7 @@ Follow these conventions in all Rust code:
    ```
 4. **JSON serialization**: Use `serde_json` with `#[derive(Serialize)]` structs, not manual string building
 5. **Precompute at startup**: For static/rarely-changing responses, compute once at startup and store in `AppState`
-6. **Unique placeholders**: When injecting content into HTML, use distinctive markers like `__NARROWIT_OG_TAGS__` that won't accidentally match other content
+6. **Unique placeholders**: When injecting content into HTML, use distinctive markers like `__PERFECT_POSTCODES_OG_TAGS__` that won't accidentally match other content
 
 ## Key Implementation Details
 
@@ -317,7 +317,7 @@ Follow these conventions in all Rust code:
 - **Server-side AABB filtering**: Both `/api/hexagons` and `/api/postcodes` filter results by bounding-box intersection with query bounds. Hexagons use `h3_cell_bounds()` (h3o returns degrees, not radians). Postcodes compute polygon AABB from vertices. See `bounds_intersect()` in `parsing/bounds.rs`.
 - **GridIndex returns slightly more than requested**: The 0.01° grid cells mean properties up to ~1km outside the viewport may be returned. The AABB filter in the route handlers catches these extras.
 - **POI proximity**: Uses 0.05° grid (~5km cells) to reduce candidates before haversine distance check
-- **OG tag injection**: Uses `<meta name="x-og-placeholder" content="__NARROWIT_OG_TAGS__"/>` placeholder in HTML, replaced at runtime by middleware
+- **OG tag injection**: Uses `<meta name="x-og-placeholder" content="__PERFECT_POSTCODES_OG_TAGS__"/>` placeholder in HTML, replaced at runtime by middleware
 
 ## Rust Performance Patterns (server-rs)