feat(aidd-context): AI commits on its own during implementation

[blafourcade]

An AI implementing a plan should commit as it goes, on its branch, instead of leaving one unreviewable blob at the end.

Scope

• Commit cycle guidelines in the project-memory vcs.md template: when the AI commits, at what granularity, and what it never commits.

Acceptance criteria

• A generated vcs.md states when the AI commits on its own.
• The rule holds for a branch, never for the default branch.

Implemented in PR #397.