[codex] Add freebuff access tier analytics

[brandonkachen]

Summary

• Add accessTier: 'full' | 'limited' to freebuff chat completion analytics after country/privacy classification.
• Move the sampled chat completions request event until after freebuff access classification so it receives the same analytics defaults.
• Add tests covering full-tier success events and limited-tier validation events.

Validation

• bun test web/src/app/api/v1/chat/completions/__tests__/completions.test.ts

Note: the focused test run passes, with an existing postgres reconnect TimeoutNegativeWarning emitted during the suite.