[Claude] 4.2: Add SerenDB API key flow documentation

[taariq]

Parent: #28

Depends on: All Phase 1-3 tasks

Task

Update README.md with documentation for the API-key flow feature.

File to Modify

README.md

What to Add

Add a new section "SerenDB Integration" documenting:

1. Setup - How to get and set API key
2. Usage - How to use init/sync without --target
3. What happens (interactive picker, auto-create DBs, state persistence)
4. Legacy mode - How to still use explicit connection strings

See docs/plans/api-key-flow-implementation.md Task 4.2 for the content.

How to Test

• Review README renders correctly on GitHub
• Test the documented commands work as described

Commit Message

docs: Add SerenDB API key flow documentation

[taariq]

Documentation added to README.md with two options for SerenDB users: Option 1 (Interactive Project Selection) and Option 2 (Explicit Connection String). Also fixed various compilation issues in tests during the review.