add support for basic auth in multi-user mode

[marioeljuga]

Description

Adds Basic authentication support to multi-user HTTP transport mode. Enables users to authenticate via Authorization: Basic <token> headers alongside existing OAuth and PAT methods.

Fixes: #

Changes

• Added basic auth type handling in dependencies.py with base64 credential decoding
• Extended UserTokenMiddleware in main.py to process Basic auth headers
• Fixed auth detection logic in environment.py (elif → if)

Testing

• Unit tests added/updated
• Integration tests passed
• Manual checks performed: Tested with Basic auth headers for Confluence operations in multi-user setup.

Checklist

• Code follows project style guidelines (linting passes).
• Tests added/updated for changes.
• All tests pass locally.
• Documentation updated (if needed).

[github-actions]

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