Add operation flags using `git-notes` for special ChronDB events

[avelino]

To make it easier to track critical or non-standard operations, ChronDB should automatically attach flags via git-notes to identify events such as:

• bulk-load
• rollback
• migration
• automated-merge

Goal:
Enhance Git history with semantic flags that mark special events for observability, analytics, or human inspection.

Acceptance Criteria:

• Special operations are detected internally and trigger note creation
• Flags are attached via git-notes in a structured format (e.g., JSON or plain array)
• Notes are added regardless of the interface/protocol used (REST, CLI, Redis, etc.)
• Multiple flags per commit are supported if applicable

Example note (output of git notes show <commit>):

{
  "flags": ["bulk-load", "migration"]
}