#23341: feat: prioritize lastGood auth profile over round-robin ordering

## Summary When no explicit `auth.order` is configured, prioritize the `lastGood` profile instead of pure round-robin ordering. This avoids wasting API attempts on exhausted profiles, especially when cooldown detection is unreliable (e.g. Gemini). ## Problem The current round-robin strategy (`orderProfilesByMode`) sorts profiles by type preference and `lastUsed` timestamp. When a profile's quota is exhausted but cooldown is not triggered (common with some providers), every request wastes one attempt on the dead profile before falling back. ## Solution After the round-robin sort, check if there is a `lastGood` profile recorded. If so, move it to the front of the list — unless it is in cooldown. This ensures: - **Normal operation**: The last known-good profile is used first, avoiding unnecessary failures - **Quota exhaustion**: After the first failure, fallback succeeds and `lastGood` updates to the working profile — all subsequent requests skip the dead profile - **Cooldown still respected**: `lastGood` in cooldown remains deprioritized - **`preferredProfile` unchanged**: Explicit user choice still takes highest priority - **Explicit `auth.order` unchanged**: When users configure their own order, the behavior is not affected ## Changes - `src/agents/auth-profiles/order.ts`: Add lastGood prioritization in the no-explicit-order path - Updated existing test to reflect the new expected behavior <!-- greptile_comment --> <h3>Greptile Summary</h3> Added `lastGood` profile prioritization to the round-robin ordering logic when no explicit `auth.order` is configured. This optimization reduces wasted API attempts on exhausted profiles when cooldown detection is unreliable. **Key changes:** - `lastGood` profile now moves to front of round-robin order when not in cooldown - `preferredProfile` still takes highest priority (user choice preserved) - Explicit `auth.order` configuration remains unchanged - Updated test to reflect new behavior <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - The implementation correctly prioritizes `lastGood` profile while preserving existing priority guarantees (`preferredProfile` > `lastGood` > round-robin). The cooldown check prevents using failed profiles. The change is well-contained, has clear motivation, and the test was updated appropriately. No logical errors or security issues identified. - Consider renaming the test file to match the new behavior, and adding test coverage for `preferredProfile` vs `lastGood` interaction and cooldown handling _{Last reviewed commit: d7dff95} <!-- greptile_other_comments_section --> _{(3/5) Reply to the agent's comments like "Can you suggest a fix for this @greptileai?" or ask follow-up questions!} <!-- /greptile_comment -->