feat(procedures): document merge workflow preference

## Summary

Create a formal procedure documenting the preference for merge commits over squash commits in the git workflow.

## Rationale

- **Preserve commit history**: Individual commits provide valuable context for future analytics
- **Maintain granularity**: Each commit represents a distinct change with its own message and principle
- **Enable better debugging**: Can pinpoint exact commits that introduced changes
- **Support commit analytics**: Full history enables analysis of development patterns

## Procedure Details

Should document:
- Use `gh pr merge --merge --delete-branch` as standard
- Never use `--squash` unless explicitly required
- Benefits of preserving full commit history
- How this supports the versioning mindset principle

## Implementation

Add to `knowledge/procedures/git-workflow.md` or create `merge-workflow.md`

Principle: transparency-in-agent-work

Read knowledge/procedures/git-workflow.md first, or confirm whether a separate merge-workflow.md is more consistent with the repository. Document the preferred gh pr merge --merge --delete-branch workflow, when squash merges are allowed, and how preserving commit history supports versioning mindset and transparency-in-agent-work.

Written by the indexing model from the issue text.