Refactor architecture documentation and enhance security features

- Updated architecture constraints documentation to include detailed sections on technical, organizational, regulatory, environmental, and performance constraints.
- Created separate markdown files for each type of constraint for better organization and clarity.
- Revised the architecture scope section to provide a clearer overview of the system's key areas.
- Enhanced the solution strategy documentation with detailed explanations of the client-server architecture, technology choices, trade-offs, and future considerations.
- Added comprehensive descriptions of backend and frontend components, middleware, and utilities in the architecture documentation.
- Migrated UI, templates, and styling notes to a dedicated section for better structure.
- Updated requirements.txt to include missing dependencies.
- Refactored user authentication logic in the users.py and security.py files to improve code organization and maintainability, including the integration of OAuth2 password bearer token handling.

docs/architecture/05_blocks/05_03_frontend_components.md

@@ -0,0 +1,11 @@
+---
+title: '05 — Frontend Components'
+description: 'Description of the frontend components of the CalMiner application.'
+status: draft
+---
+
+- **Templates** (`templates/`): Jinja2 templates for server-rendered HTML views, extending a shared base layout with a persistent sidebar for navigation.
+- **Static Assets** (`static/`): CSS and JavaScript files for styling and interactivity. Shared CSS variables in `static/css/main.css` define the color palette, while page-specific JS modules in `static/js/` handle dynamic behaviors.
+- **Reusable partials** (`templates/partials/components.html`): macro library that standardises select inputs, feedback/empty states, and table wrappers so pages remain consistent while keeping DOM hooks stable for existing JavaScript modules.
+  - `templates/settings.html`: Settings hub that renders theme controls and environment override tables using metadata provided by `routes/ui.py`.
+  - `static/js/settings.js`: applies client-side validation, form submission, and live CSS updates for theme changes, respecting environment-managed variables returned by the API.