feat: add Xiaomi MiMo provider

[AdityaVG13]

Summary

• Adds Xiaomi MiMo as a first-class provider across config parsing, CLI forwarding, key storage, TUI provider switching, picker UI, request shaping, docs, and examples.
• Uses Xiaomi MiMo's OpenAI-compatible endpoint defaults: https://api.xiaomimimo.com/v1 and mimo-v2.5-pro.
• Keeps CodeWhale's static Xiaomi MiMo model list focused on current V2.5 models: mimo-v2.5-pro and mimo-v2.5.
• Handles MiMo-specific request fields by sending max_completion_tokens and mapping reasoning control to MiMo's thinking field.
• Documents MiMo vision through CodeWhale's existing [vision_model] / image_analyze path and uses mimo-v2.5 for image input per Xiaomi's current image-understanding docs.
• Updates English, Chinese, and Japanese README provider examples, provider docs, config examples, and static model metadata.

Related upstream scan:

• No exact open upstream PR/issue for Xiaomi MiMo found.
• Related only: upstream issue 使用 opencode-go 无法切换其他开源模型？ Hmbown/CodeWhale#1572 references MiMo model IDs in an OpenCode-Go custom provider example, not native CodeWhale provider support.
• Prior UX references checked: upstream provider PRs feat(tui): add SiliconFlow provider Hmbown/CodeWhale#1864, [codex] Add SiliconFlow provider support Hmbown/CodeWhale#1868, [codex] Document OpenAI-compatible provider setup Hmbown/CodeWhale#1867, feat: add Volcengine provider with DeepSeek-V4-Pro/Flash support Hmbown/CodeWhale#1993 and branch names docs/provider-registry-2201-20260526, fix/1656-local-http-provider.

Testing

• cargo fmt --all -- --check
• git diff --check
• cargo check -p codewhale-tui
• cargo clippy -p codewhale-tui --all-targets --all-features (passes with existing unrelated warnings)
• cargo test -p codewhale-agent xiaomi_mimo --lib
• cargo test -p codewhale-config xiaomi_mimo --lib
• cargo test -p codewhale-secrets xiaomi_mimo --lib
• cargo test -p codewhale-cli build_tui_command_forwards_provider_keyring_env_vars_for_all_providers --lib
• cargo test -p codewhale-tui xiaomi_mimo
• cargo test -p codewhale-tui vision::tools::tests
• cargo test -p codewhale-tui reasoning_effort_uses_xiaomi_mimo_thinking_parameter_only
• cargo test -p codewhale-tui provider_capability_xiaomi_mimo_has_thinking_no_cache

Local hygiene checks:

• Added-line secret/local marker scan: 0 hits after excluding placeholders
• Dotfile/dotdir path changes: 0 changed paths
• Public hygiene packet generated outside repo
• public_hygiene_scan.py --repo-root . --mode review-only run; it reports inherited repo-wide baseline findings, but no credible new secret/personal/dotdir leak was found in this PR diff

Checklist

• Updated docs or comments as needed
• Added or updated tests where relevant
• Verified TUI behavior manually if UI changes

Notes:

• This is a fork-local staging PR for review before opening anything against Hmbown/CodeWhale.
• Full cargo test --workspace --all-features previously hit existing local/upstream-sensitive failures unrelated to Xiaomi MiMo; focused provider and vision coverage is passing.