[Positioning] Build comparison page vs. alternatives

[khelanmodi]

Goal

Help users pick the right tool, transparently.

What to ship

docs/comparison.md with a table comparing:

• documentdb-mcp (this server)
• mongodb-mcp-server (Mongo/Atlas-focused)
• Direct DocumentDB SDK usage

Across dimensions:

• Primary target backend
• Auth modes
• Security defaults (default tier, denylists, audit, pipeline-namespace gating)
• Tool count / consolidation approach
• Hosted runtime availability
• License
• Maturity

Acceptance criteria

• Honest — no FUD against alternatives.
• Linked from the README.
• Reviewed by someone neutral.

Depends on

• All four Positioning Decisions.