fix: normalize mcpServers config key to mcp and transform external MCP formats

[anandgupta42]

What does this PR do?

Fixes the config validation error when users or LLMs write MCP server config using the mcpServers key (common in Claude Code, Cursor, .mcp.json format). The strict config schema rejected this with Unrecognized key: "mcpServers", preventing the app from starting.

This PR adds a normalizeMcpConfig function that:

• Auto-normalizes top-level mcpServers → mcp with a warning log
• Transforms external MCP server format: string command + args + env → array command + environment
• Handles remote servers without explicit type field (infers from url presence)
• Always deletes mcpServers to prevent strict schema rejection (even when mcp already exists)
• Normalizes typed entries that use external field names (env, string command)

Type of change

• Bug fix (non-breaking change which fixes an issue)

Issue for this PR

Closes #638 (reported in #619)

How did you verify your code works?

• 5 new tests covering: string command format, array command format, both-keys conflict resolution, remote server normalization, typed entry with external field names
• All 7217 existing tests pass (0 failures)
• Typecheck passes
• Marker Guard passes (bun run script/upstream/analyze.ts --markers --base main --strict)
• Multi-model code review (6 models: Claude, GPT 5.2 Codex, Gemini 3.1 Pro, Kimi K2.5, MiniMax M2.5, GLM-5) — all critical/major findings addressed

Checklist

• My code follows the project's coding standards
• I have performed a self-review of my code
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes
• I have added altimate_change markers to upstream-shared files

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 8e04c111-3ba6-484a-a8b0-bd203839ffaf

📥 Commits

Reviewing files that changed from the base of the PR and between dd0c323 and 4ca0b3f.

📒 Files selected for processing (2)

• packages/opencode/src/config/config.ts
• packages/opencode/test/config/config.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/normalize-mcpservers-config-key

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