feat(build): consolidate 6 packages into single mamba-mcp with extras

[sequenzia]

BREAKING CHANGE: Replaced 6 separate PyPI packages with a single mamba-mcp package using optional extras for modular installation.

Directory restructuring:

• Source: packages/*/src/ → src/ (6 modules, all import paths preserved)
• Tests: packages/*/tests/ → tests/{core,client,pg,fs,hana,gitlab}/
• Examples: packages/mamba-mcp-client/examples/ → examples/
• Removed packages/ directory and 6 per-package pyproject.toml files

Package changes:

• Single pyproject.toml with extras: [client], [pg], [fs], [hana], [gitlab], [all]
• Single hatch-vcs version at src/mamba_mcp_core/_version.py
• All 5 sub-module init.py files import version from core
• Added mamba-mcp CLI alias for the client
• Eliminated UV workspace in favor of flat src layout

Code fixes:

• Upgraded str+Enum to StrEnum in client (OutputFormat, LogLevel, TransportType, MessageDirection)
• Fixed import sorting (first-party reclassification after consolidation)
• Updated 7 test files with corrected conftest import paths

CI/CD:

• ci.yml: uses uv sync --all-extras, matrix tests by suite subdirectory
• release.yml: single uv build instead of 6-package loop

Documentation:

• Updated CLAUDE.md, README.md, CHANGELOG.md, and 4 MkDocs pages
• Preserved per-package READMEs in docs/packages/