Add production-grade rate limiting plan

[sardorcodev]

Plan production-grade rate limiting for auth and analyze endpoints.

Scope:

• Identify endpoints that need rate limiting.
• Propose local/dev and hosted deployment strategies.
• Consider login brute-force protection.
• Do not add distributed infrastructure prematurely.

Acceptance criteria:

• Rate limiting plan is documented.
• Auth and analyze endpoint risks are listed.
• Future implementation steps are defined.