docs: Add comprehensive rustdoc for pages and db modules, marking plan items done

Co-authored-by: aider (openai/andrew/openrouter/sonoma-sky-alpha) <aider@aider.chat>

src/db.rs

@@ -456,6 +456,34 @@ pub fn query_upsert_meta(conn: &Connection, meta: Meta) -> Result<()> {
     Ok(())
 }
 
+/// Stores a metadata entry, deleting it if the value is empty.
+///
+/// Handles both insertion/update and deletion based on value presence.
+///
+/// # Arguments
+///
+/// * `conn` - Database connection.
+/// * `meta` - Metadata entry to store (empty value triggers deletion).
+///
+/// # Returns
+///
+/// * `Result<()>` - Success or error if the operation fails.
+///
+/// # Errors
+///
+/// * Database errors during insert/update/delete.
+///
+/// # Examples
+///
+/// ```
+/// // Insert new metadata
+/// let meta = Meta { id: 1, name: "source".to_string(), value: "cli".to_string() };
+/// db::store_meta(&conn, meta)?;
+///
+/// // Delete metadata with empty value
+/// let meta = Meta { id: 1, name: "temp".to_string(), value: "".to_string() };
+/// db::store_meta(&conn, meta)?;
+/// ```
 /// Stores a metadata entry, deleting it if the value is empty.
 ///
 /// Handles both insertion/update and deletion based on value presence.