P14-T3: Reconcile declared Python support with tested matrix

[SoundBlaster]

Description

Align declared Python compatibility with the CI-tested matrix.

Changes:

• Set requires-python to >=3.9.
• Removed Python 3.7/3.8 classifiers; kept 3.9–3.12.
• Updated README Python badge and prerequisites to 3.9+.
• Updated installation guide prerequisites to Python 3.9+.
• Archived FLOW artifacts for P14-T3.

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactoring
• CI/CD improvement

Quality Gates

Before submitting, ensure all quality gates pass:

make check

Or run individually:

• make test - All tests pass with ≥90% coverage
• make lint - No linting errors
• make format - Code is properly formatted
• make typecheck - Type checking passes
• make doccheck - Documentation is synced with DocC (if docs changed)

make test equivalent run details:

• pytest / pytest --cov each have one pre-existing local-environment failure: tests/unit/test_broker_transport.py::TestSocketPermissions::test_socket_created_with_0600_permissions (OSError: AF_UNIX path too long).
• Coverage is 91.33%.

Documentation Sync

If you modified files in docs/, ensure corresponding DocC files are also updated:

docs/ file	DocC file
docs/installation.md	mcpbridge-wrapper.docc/Installation.md
docs/cursor-setup.md	mcpbridge-wrapper.docc/CursorSetup.md
docs/claude-setup.md	mcpbridge-wrapper.docc/ClaudeCodeSetup.md
docs/codex-setup.md	mcpbridge-wrapper.docc/CodexCLISetup.md
docs/troubleshooting.md	mcpbridge-wrapper.docc/Troubleshooting.md
docs/architecture.md	mcpbridge-wrapper.docc/Architecture.md
docs/environment-variables.md	mcpbridge-wrapper.docc/EnvironmentVariables.md
README.md	mcpbridge-wrapper.docc/mcpbridge-wrapper.md

• Documentation changes are synced with DocC catalog (or N/A)

Testing

• Added/updated tests for new functionality
• All tests pass locally
• Manually tested the changes

Checklist

• Code follows the project's style guidelines
• Self-review completed
• Comments added for complex code
• Documentation updated (if needed)
• No new warnings generated
• PR title is descriptive