adj: add 4.1 flash and price change 0910

[ChthoIly]

Summary

更新 4.1 flash 模型的计费信息，更新 0910 的 API 计费下调

Verification

• npm run verify
• npm pack --dry-run
• Clean-profile DSH installation tested when bundle, inject, slot, or route behavior changed
• No API keys, account data, private sessions, logs, or generated lib/ files included
• CHANGELOG.md updated for user-visible changes

[Max-Samson]

Hi @ChthoIly
Thanks a lot for this PR — it's clean and spot-on. I cross-checked every number against both the zh-CN and EN official pricing pages:

• ✅ All figures match exactly (Flash off-peak/peak CNY 0.02 / 1 / 4 → 0.04 / 2 / 8, USD 0.003 / 0.15 / 0.6 → 0.006 / 0.3 / 1.2); V4-Pro correctly left unchanged.
• ✅ Nice touch keeping deepseek-v4-flash / deepseek-v4-flash-vision-exp as aliases pointing at the same FLASH_PRICING, so historical sessions don't suddenly become "unpriced models"; the fallback price is updated too.
• ✅ Peak-hours rule (Mon–Fri 09:00–12:00, 14:00–18:00 Beijing) matches footnote (3).
• ✅ verifiedAt maps exactly to 2026-09-10.
• ✅ Tests fully updated — 40/40 passing locally, including alias-equivalence and prefix-match assertions.

I'll merge this into main; I'll take care of the CHANGELOG entry and the version bump / npm release, so no extra work needed from you.

Really appreciate the accuracy contribution — it matters a lot for anyone using this plugin to track spend 🙏