Fix CI quality gates and cross-platform Bash selection

[PRINCE2-AI]

What changed

• format the Python codebase and resolve all Ruff findings
• pin CI-only tooling in requirements-dev.txt
• make Ruff and MyPy non-mutating, blocking quality gates
• update checkout/setup-python Actions and restrict workflow permissions
• select Git Bash explicitly on Windows instead of the WSL launcher
• strengthen frozen-config and shell tests

Root cause

The workflow ran ruff check --fix inside CI, but remaining non-fixable lint findings stopped the job before Black, MyPy, or Pytest could run. Windows also resolved bash to the WSL launcher even when Git Bash was installed.

Validation

• ruff check .
• black --check .
• mypy . (27 source files, 0 issues)
• pytest -q (156 passed)

[Copilot]

Pull request overview

This PR tightens CI “quality gate” behavior (non-mutating, blocking Ruff/MyPy/Black), pins CI-only tooling, and improves Windows Bash resolution by explicitly preferring Git Bash (avoiding accidental selection of the WSL launcher). It also includes broad formatting/typing cleanups and strengthens tests around tools and frozen config behavior.

Changes:

• Make CI lint/typecheck steps non-mutating and blocking; restrict workflow permissions; install pinned dev tools via requirements-dev.txt.
• Add Windows-aware Bash executable resolution for bash_tool.
• Formatting, typing modernizations (PEP 604 unions), and test hardening/cleanup across the Python codebase.

Reviewed changes

Copilot reviewed 27 out of 27 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tools.py	Adds Windows Git Bash detection for bash_tool; minor robustness tweaks in file tool path handling and typing.
tests/test_tools.py	Updates tool tests to validate Bash selection and applies formatting cleanup.
tests/test_task.py	Import ordering/formatting cleanup.
tests/test_rate_limiter.py	Removes unused imports / formatting cleanup.
tests/test_plugins.py	Removes unused imports; adjusts broken-plugin test string quoting.
tests/test_persistence.py	Reorders imports and formatting cleanup.
tests/test_metrics.py	Import ordering/formatting cleanup.
tests/test_main.py	Simplifies “no exception” tests and formatting cleanup.
tests/test_exceptions.py	Import ordering/formatting cleanup.
tests/test_cost_tracker.py	Formatting cleanup in assertions and __main__ block.
tests/test_context.py	Formatting cleanup in __main__ block.
tests/test_config.py	Strengthens frozen-dataclass assertion by catching FrozenInstanceError specifically.
task.py	Typing/formatting updates; adopts PEP 604 unions.
security.py	Typing modernization and clearer multi-line error strings.
requirements-dev.txt	Introduces pinned CI/dev-only tooling via a dedicated requirements file.
rate_limiter.py	Formatting cleanup.
plugins.py	Formatting cleanup.
persistence.py	Typing modernization, improved exception chaining, and formatting cleanup.
metrics.py	Typing modernization and formatting cleanup; expands one-line properties for clarity.
main.py	Formatting cleanup and minor import reordering.
logger.py	Formatting cleanup for regex patterns and formatter setup.
exceptions.py	Formatting cleanup in exception definitions/messages.
cost_tracker.py	Import ordering, typing modernization, and formatting cleanup.
context.py	Typing modernization and formatting cleanup of long strings.
config.py	Formatting cleanup; expands config sets for readability; no functional config intent change beyond layout.
agent.py	Import ordering and formatting cleanup.
.github/workflows/ci.yml	Updates workflow triggers/permissions and makes Ruff/MyPy blocking; installs dev toolchain from requirements-dev.txt.

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