feat: implement collections book picker with Alpine.store

Add multi-select book picker modal for collections using Alpine.js patterns:
- Alpine.store("bookPicker") for global state persistence across HTMX updates
- Book selection state maintained as Set<string> to survive DOM swaps
- Modal with filterable book grid (search, author, genre, series)
- Bulk add books to collection functionality

Templates:
- collections.templ: Add book picker modal with Alpine component bindings
- Remove old inline-JS modal (replaced with declarative Alpine markup)

TypeScript:
- web/src/bookPicker.ts: New module with Alpine.store and Alpine.data definitions
- web/src/main.ts: Import bookPicker module
- web/src/collections.ts: Remove old modal functions (replaced by Alpine)

This implements the Book Picker Modal feature from the collections system,
following SSR-first Alpine.js patterns with HTMX for dynamic updates.

Fixes "Add Books" button being disabled - modal now fully functional.

web/src/main.ts

@@ -2,11 +2,12 @@ import "./alpine";
 import { Alpine } from "./alpine";
 
 import "./admin";
-import "./api";
 import "./analytics";
+import "./api";
 import "./api-explorer";
 import "./api-explorer-docs";
 import "./bookPicker";
+import "./bookshelf";
 import "./collection-rules";
 import "./collections";
 import "./conflicts";
@@ -19,8 +20,8 @@ import "./events";
 import "./header";
 import "./index";
 import "./library";
-import "./login";
 import "./linking";
+import "./login";
 import "./password_validation";
 import "./profile";
 import "./profile-modal";