refactor: rebrand OpenCode to MiMo Code in user-facing strings (#8, #14, #19, #29)

[czs654]

Summary

Rebrand 'OpenCode' to 'MiMo Code' in all user-facing strings across the codebase. This addresses issues XiaomiMiMo#8, XiaomiMiMo#14, XiaomiMiMo#19, and XiaomiMiMo#29.

Changes (14 files, 41 replacements)

Documentation:

• CONTRIBUTING.md — title, section headers, and all prose references to "OpenCode" → "MiMo Code"
• packages/desktop/README.md — title and description

Desktop App:

• packages/desktop/electron-builder.config.ts — productName, protocol names, appId for dev channel
• packages/desktop/package.json — author name
• packages/desktop/src/main/menu.ts — app label, "OpenCode Documentation" → "MiMo Code Documentation"

Server & Auth:

• packages/opencode/src/mcp/oauth-provider.ts — OAuth client_name
• packages/opencode/src/mcp/oauth-callback.ts — authorization page titles
• packages/opencode/src/plugin/codex.ts — Codex authorization page titles
• packages/opencode/src/acp/agent.ts — login label, agent name

UI & Schema:

• packages/ui/src/assets/favicon/site.webmanifest — name, short_name
• packages/ui/src/components/favicon.tsx — apple-mobile-web-app-title meta
• packages/ui/src/theme/desktop-theme.schema.json — title, description

Other:

• LICENSE — copyright holder normalization
• packages/sdk/js/src/v2/client.ts — server name in error message

What is NOT changed (intentionally)

• GitHub URLs (anomalyco/opencode) — infrastructure change requiring coordination
• opencode.ai domain URLs — infrastructure change
• Internal package names (@mimo-ai/*) — already migrated
• CLI binary names — separate change
• Internal identifiers/variables — not user-facing

Fixes XiaomiMiMo#8
Fixes XiaomiMiMo#14
Fixes XiaomiMiMo#19
Fixes XiaomiMiMo#29