M1: Implement documented local skip controls

[dbrosio3]

Goal

Implement the documented one-push skip controls for the local Pushgate runner and wrapper.

User value

Developers can intentionally bypass all local Pushgate work or skip only the AI layer without losing the fast deterministic checks.

Implementation notes

• Keep native git push --no-verify documented as Git's broad hook bypass.
• Make pushgate pre-push read the one-command Git config paths: pushgate.skip-all-checks and pushgate.skip-ai-check.
• Implement pushgate push --skip-all-checks and pushgate push --skip-ai-check as friendly wrappers over the matching Git config paths.
• Ensure skip-ai-check retains deterministic checks and only bypasses local AI.
• Ensure skip-all-checks bypasses both deterministic checks and local AI when the hook still runs.
• Define precedence, terminal output, and tests for whole-runner and AI-only skip paths.

Risks / tradeoffs

• Git's native --no-verify bypass cannot be observed by the hook because the hook never runs.
• Persistent Git config or environment aliases can make skip behavior less visible if precedence is not explicit.

Suggested priority

P0

Milestone

M1: Deterministic local gate

TBD considerations

• Whether persistent git config pushgate.skip-* values are supported or only one-command overrides are part of the public contract.
• Whether environment-variable aliases remain available for automation even though public examples use Git's temporary config channel.

Acceptance criteria

• git -c pushgate.skip-all-checks=true push skips local deterministic checks and local AI when Pushgate is invoked.
• git -c pushgate.skip-ai-check=true push skips local AI while deterministic checks still run.
• pushgate push --skip-all-checks and pushgate push --skip-ai-check map to the same behavior.
• Skip output is visible and tests cover precedence and both skip scopes.