feat(phase-1): Complete foundation setup

- Add User model and authentication system with JWT cookies
- Implement login/logout routes and protected dashboard
- Add Alembic database migration configuration
- Add create_admin.py script for initial user setup
- Make ContentGenerator and ImageGenerator lazy-initialized
- Add comprehensive API keys setup documentation
- Fix startup errors when services unavailable

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/services/image_generator.py

@@ -24,10 +24,22 @@ class ImageGenerator:
             loader=FileSystemLoader(self.templates_dir)
         )
 
-        self.hti = Html2Image(
-            output_path=str(self.output_dir),
-            custom_flags=['--no-sandbox', '--disable-gpu']
-        )
+        self._hti = None
+
+    @property
+    def hti(self):
+        """Lazy initialization de Html2Image."""
+        if self._hti is None:
+            try:
+                self._hti = Html2Image(
+                    output_path=str(self.output_dir),
+                    custom_flags=['--no-sandbox', '--disable-gpu']
+                )
+            except FileNotFoundError:
+                raise RuntimeError(
+                    "Chrome/Chromium no encontrado. Instala Chrome o ejecuta en Docker."
+                )
+        return self._hti
 
     def _render_template(self, template_name: str, variables: Dict) -> str:
         """Renderizar una plantilla HTML con variables."""