Support structured context fields in logging

[ephur]

Enhance the log() function to accept and output structured key-value fields like event=plan_start, deployment=foo. In plain output, append these; in JSON, include as structured fields.

[ephur]

🤖 Initial triage (AI-generated):

This feature would improve observability by allowing contextual data (e.g., event=plan_start) to be included in log output. The current log() function already accepts **kwargs, so structured fields can be passed directly.

⚙️ Suggested approach:

• For JSON: include context fields at the root level
• For plain: append key=value inline (e.g., INFO: event=plan_start foo=bar)
• Consider filtering or key casing consistency

🧪 Ensure no collisions with reserved fields like msg, level, etc.

Disclaimer: This triage is AI-generated and may need refinement.