feat: add schema versioning table and improve migration logic ...

- Introduced 'internal_metadata' table to track database version.
- Updated migrate_025_to_030 to use 'internal_metadata' presence as a version indicator.
- Updated 03_database_specification.md with the new table.
- Recorded in journal 20260223-0019.

feat: add MIME type support to documents ...

- Added 'mime' column to 'documents' table in db.rs.
- Implemented automatic MIME detection in mcp.rs 'add_item_text' tool.
- Updated search and retrieval tools in mcp.rs to return 'mime' information.
- Refreshed 03_database_specification.md to reflect the new column.
- Recorded work in journal 20260223-0015.

feat: normalize database schema for document-chunk separation (Issue-2) ...

- Added 'documents' table for metadata.
- Refactored 'items' table for chunk storage.
- Updated MCP tools (add_item_text, search_text, etc.) to support the new schema.
- Updated technical documentation.

Docs: Modernize all specification documents to align with LSA-based architecture and new directory structure

Refactor: reorganization of root and source directories and fix Error 1412