chore: stabilize Python support

[Intrinsical-AI]

Summary

• Pin supported Python range to >=3.11,<3.13.
• Refresh uv.lock for Python 3.11/3.12 only.
• Update README Python badge and clean up bootstrap progressbar typing.

Validation

• git diff --check
• uv run ruff check src tests
• UV_CACHE_DIR=/tmp/uv-cache uv run --group lint --group test --extra server mypy src
• UV_CACHE_DIR=/tmp/uv-cache PYTHONPATH=src uv run --group lint lint-imports
• UV_CACHE_DIR=/tmp/uv-cache uv run --group test --extra server pytest -q

Result: 698 passed, 4 skipped; coverage 87.19%.