docs: keep environment configuration in sync

[Davidson3556]

What does this change?

Configuration is now documented according to the binary that actually reads it.

• The README separates settings shared by both binaries from the settings used only by molecare-ops-mcp.
• HOW_MCP_WORKS.md now shows separate public and operations server configurations.
• Unsupported ontology and Feast variable names have been removed.
• MCP_HEALTH_PORT has been added to .env.example with its precedence over PORT explained.
• Ops-only MLflow and AWS settings have been removed from the public MCP Registry entry.

The new regression test follows static and dynamic local imports from both entrypoints, collects their process.env usage, and verifies that:

• .env.example contains exactly the supported variables
• the README documents every variable in the correct public/shared/operations section
• server.json does not advertise settings that only the operations server can read

Related issue

Fixes #93

Checklist

• npm run build passes
• Server starts and existing tools remain unchanged
• Works in mock mode (no credentials configured)
• No secrets, real hostnames, account IDs, or personal data added
• No patient images added — including in tests
• No medical content changed

Does this change a tool's response shape?

No. This only corrects configuration documentation and Registry metadata.

Validation

• npm test — 83/83 tests pass
• git diff --check

[YauhenBichel]

Great test, thank you! It found one real gap it cannot see yet: src/privacy-gate.ts reads env.PRIVACY_GATE_URL and env.PRIVACY_GATE_TIMEOUT_MS (not process.env.X). Could you add both to README.md and .env.example, and make the test match the env.X form too?