fix(xiaomi-token-plan): remove mimo-v2-omni (not served by token-plan endpoints)

[kelvinq]

The three xiaomi-token-plan-* providers list mimo-v2-omni, but their endpoints don't serve it. Requests return:

{"error": {"code": "400", "message": "Param Incorrect", "param": "Not supported model mimo-v2-omni"}}

mimo-v2-omni is pay-as-you-go only and lives under providers/xiaomi/. The token-plan endpoints serve only the v2.5 family.

Probed the SGP token-plan endpoint on 2026-07-06:

• GET /v1/models returns 6 models, all v2.5-family: mimo-v2.5, mimo-v2.5-asr, mimo-v2.5-pro, mimo-v2.5-tts, mimo-v2.5-tts-voiceclone, mimo-v2.5-tts-voicedesign. No mimo-v2-omni.
• POST /v1/chat/completions with mimo-v2.5-pro returns HTTP 200 (positive control).
• POST /v1/chat/completions with mimo-v2-omni returns HTTP 400 with the body above.

I only probed the SGP endpoint live. The three token-plan providers share one upstream catalog. The ams and sgp model files are symlinks to the cn file, so this removes the model from all three in one change.

This mirrors the earlier mimo-v2-flash removal (earendil-works/pi#5075), which removed a pay-as-you-go-only model from the token-plan providers. That entry also came up in a comment, so this PR updates the three provider.toml comments that mentioned "V2 Omni".

Tracked upstream in earendil-works/pi#6204.

Validated with bun validate.

[nathannli]

don't think this is right. you should be deprecating models when they're no longer provided, not deleting them:

status (optional): String — Supported status:
alpha - Indicate the model is in alpha testing
beta - Indicate the model is in beta testing
deprecated - Indicate the model is no longer served by the provider's public API

[kelvinq]

Hi @nathannli. They have been deprecated since 30 Jun 2026. See: https://mimo.mi.com/docs/en-US/quick-start/summary/model

[rekram1-node]

generally we have been making models as deprecated if they have been deprecated but still serve traffic but if the model is completely dead and wont work at all we drop it