feat(provider): upgrade minimax preset to MiniMax-M3

[octo-patch]

Summary

升级 minimax provider preset，把默认模型从 MiniMax-M2.7 切到新一代的 MiniMax-M3，并清理过期的 M2.5 / M2.1 / M2 条目；保留 MiniMax-M2.7 和 MiniMax-M2.7-highspeed，方便已经在使用上一代模型的用户继续锁定。

影响范围

• server / provider — src/server/config/providerPresets.json、src/utils/model/modelContextWindows.ts：default model + 内置 context window 表统一升级到 M3，删掉 M2.5 / M2.1 / M2 条目
• server tests — provider-presets.test.ts / providers-real.test.ts / thinking.test.ts 改成断言新的默认模型 MiniMax-M3
• docs — .env.example、中英版 docs/guide/env-vars.md、docs/guide/third-party-models.md：示例 / 推荐配置改为 M3，并在 zh/en 模型表里同时列出 M3 + M2.7 + M2.7-highspeed
• scripts — scripts/repro-issue-247-real.ts 的默认 REPRO_MODEL_ID 改成 MiniMax-M3

未触及 base URL、TTS 或其他 provider；MiniMax-M2.7 仍保留，使用者只是默认值变了。

测试说明

• bun test src/server/__tests__/provider-presets.test.ts — 7 pass
• bun test src/server/__tests__/providers-real.test.ts — 6 pass（连通性 case 因没有真实 key 报"login fail"，是预期内的离线行为）
• bun test src/utils/__tests__/thinking.test.ts — 8 pass
• bun test src/services/compact/autoCompact.test.ts — 5 pass（M2.7 仍在内置表里，原断言不需要改）
• bun test src/tools/WebSearchTool/backend.test.ts — 6 pass
• bun test scripts/quality-gate/providerTargets.test.ts — 5 pass

未跑真实模型 baseline / bun run verify 全套；本机没有 MiniMax-M3 API Key，需要维护者在合并前用真实 key 跑一遍 bun run quality:smoke --provider-model minimax:main:minimax-main 确认连通性。

剩余风险

• 假设 M3 的 context window 和 M2.7 一样是 204_800；如果官方上线后实际窗口不同，providerPresets.json 和 modelContextWindows.ts 里两处 204800 需要同步调整
• desktop/src/__tests__/generalSettings.test.tsx、scripts/quality-gate/providerTargets.test.ts、fixtures/e8c7b0.json 里仍残留 MiniMax-M2.7-highspeed 字符串，但都是 fixture / 解析测试用的占位符，跟"哪个是默认模型"无关，故未改
• bun run verify 全量门禁未跑（本仓 e2e 需要 macOS 环境 + 实际 API Key），上述定向单测均通过

[github-actions]

PR quality triage

Changed areas: area:cli-core, area:docs, area:server

CLI core policy: Blocked by policy until a maintainer applies allow-cli-core-change and approves the PR.

Missing-test policy: No missing-test policy block detected.

Coverage baseline policy: No coverage-baseline policy block detected.

CLI core files:

• src/utils/__tests__/thinking.test.ts
• src/utils/model/modelContextWindows.ts

Coverage policy files:

• none

Expected checks:

• change-policy
• desktop-checks
• server-checks
• desktop-native-checks
• docs-checks
• coverage-checks

Test coverage signals:

• Agent/model runtime path changed: use mock/request-shape tests in PR and maintainer live-model smoke before release.

Risk notes:

• Provider/search behavior changed: PR gate uses mock tests; live-provider tests stay maintainer-only.

Hard merge gates still come from GitHub Actions, not AI review.

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@dosubot review this PR for changed-area risk, missing tests, docs impact, desktop startup risk, and CLI core impact.