Add detailed SQLAlchemy models, navigation metadata, enumerations, Pydantic schemas, monitoring, and auditing documentation

- Introduced SQLAlchemy models for user management, project management, financial inputs, and pricing configuration.
- Created navigation metadata tables for sidebar and top-level menus.
- Cataloged enumerations used across ORM models and Pydantic schemas.
- Documented Pydantic schemas for API request/response validation, including authentication, project, scenario, import, and export schemas.
- Added monitoring and auditing tables for performance metrics and import/export logs.
- Updated security documentation to reflect changes in data model references.

architecture/08_concepts/02_data_model/02_navigation.md

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+# Navigation Metadata
+
+This page details the navigation metadata tables that drive the Calminer sidebar and top-level menus. It was split from `02_data_model.md` to isolate runtime navigation behaviour from the broader ORM catalogue.
+
+## NavigationGroup
+
+Represents a logical grouping of navigation links shown in the UI sidebar or header.
+
+**Table:** `navigation_groups`
+
+| Attribute    | Type         | Description                                     |
+| ------------ | ------------ | ----------------------------------------------- |
+| id           | Integer (PK) | Primary key                                     |
+| slug         | String(64)   | Unique slug identifier                          |
+| title        | String(128)  | Display title                                   |
+| description  | Text         | Optional descriptive text                       |
+| match_prefix | String(255)  | URL prefix used to auto-expand in UI            |
+| weighting    | Integer      | Ordering weight                                 |
+| icon_name    | String(64)   | Optional icon identifier                        |
+| feature_flag | String(64)   | Optional feature flag for conditional rendering |
+| created_at   | DateTime     | Creation timestamp                              |
+| updated_at   | DateTime     | Last update timestamp                           |
+
+**Relationships:**
+
+- `links`: One-to-many with NavigationLink
+
+## NavigationLink
+
+Individual navigation entry that may have an associated feature flag or role restriction.
+
+**Table:** `navigation_links`
+
+| Attribute     | Type                                | Description                                          |
+| ------------- | ----------------------------------- | ---------------------------------------------------- |
+| id            | Integer (PK)                        | Primary key                                          |
+| group_id      | Integer (FK → navigation_groups.id) | Parent navigation group                              |
+| parent_id     | Integer (FK → navigation_links.id)  | Optional parent link (for nested menus)              |
+| slug          | String(64)                          | Unique slug identifier                               |
+| title         | String(128)                         | Display title                                        |
+| description   | Text                                | Optional descriptive text                            |
+| href          | String(255)                         | Static fallback URL                                  |
+| match_prefix  | String(255)                         | URL prefix for expansion                             |
+| feature_flag  | String(64)                          | Optional feature flag for conditional rendering      |
+| required_role | String(64)                          | Optional role required to view the link              |
+| weighting     | Integer                             | Ordering weight within the parent scope              |
+| icon_name     | String(64)                          | Optional icon identifier                             |
+| metadata      | JSON                                | Additional configuration (e.g. legacy route aliases) |
+| created_at    | DateTime                            | Creation timestamp                                   |
+| updated_at    | DateTime                            | Last update timestamp                                |
+
+**Relationships:**
+
+- `group`: Many-to-one with NavigationGroup
+- `parent`: Many-to-one self-reference
+- `children`: One-to-many self-reference
+
+## Seeding and Runtime Consumption
+
+- **Seed script:** `scripts/init_db.py` provisions baseline groups and links, including nested scenario calculators and role-gated admin entries.
+- **Service layer:** `services/navigation.py` maps ORM entities into response DTOs, resolves contextual URLs for projects and scenarios, and applies feature flag as well as role filters.
+- **API exposure:** `routes/navigation.py` serves the `/navigation/sidebar` endpoint, combining seeded data with runtime context to produce navigation trees consumed by the frontend.
+- **Testing:** `tests/services/test_navigation_service.py` covers URL resolution and child filtering logic, while `tests/integration/test_navigation_sidebar_calculations.py` verifies scenario calculator entries in the API payload.
+
+Refer to the [navigation service documentation](../../../../api/README.md#navigation) for endpoint-level behaviour.