v2.0.0: Modularize project into single-responsibility packages

Replaced monolithic modules/ package with a clean architecture:

- core/       config.py, utils.py
- ai/         models.py (ResilientModel), setup.py (init_models)
- story/      planner.py, writer.py, editor.py, style_persona.py, bible_tracker.py
- marketing/  cover.py, blurb.py, fonts.py, assets.py
- export/     exporter.py
- web/        app.py (Flask factory), db.py, helpers.py, tasks.py, routes/{auth,project,run,persona,admin}.py
- cli/        engine.py (run_generation), wizard.py (BookWizard)

Flask routes split into 5 Blueprints; all templates updated with blueprint-
prefixed url_for() calls. Dockerfile and docker-compose updated to use
web.app entry point and new package paths.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/admin_spend.html

@@ -7,7 +7,7 @@
         <p class="text-muted">Aggregate cost analysis per user.</p>
     </div>
     <div class="col-md-4 text-end">
-        <a href="{{ url_for('admin_dashboard') }}" class="btn btn-outline-secondary">Back to Admin</a>
+        <a href="{{ url_for('admin.admin_dashboard') }}" class="btn btn-outline-secondary">Back to Admin</a>
     </div>
 </div>