fix(mcp): resolve every tool's secrets to plaintext so GUI IDEs authenticate

[jeff-r2026]

Problem

Even after #260 fixed the type field, remote MCP servers still failed with 401 in GUI-launched tools:

streamableHttp connect failed: ... {"error": "缺少或无效的 Bearer Token"}
connect sse failed: SSE error: Non-200 status code (401)

Root cause: teamai wrote a ${VAR} placeholder and relied on each tool to expand it. But that expansion is fragile and tool-specific — most decisively, IDEs launched from the GUI (Dock/Launchpad) never inherit the user's shell exports, so ${VAR} expands to empty → Authorization: Bearer → 401. The CLI worked only because it does inherit the shell env.

Fix

Make supportsEnvExpansion always false — every tool, every scope resolves the secret to its value and writes it verbatim. The token is then present no matter how the tool is started. Also removes the now-dead codexCanNameEveryVar helper.

tool	before	after
Claude (project)	${VAR}	plaintext
Cursor	${env:VAR}	plaintext
Codex	bearer_token_env_var	plaintext (http_headers)
CodeBuddy	${VAR}	plaintext

Docs (both languages) warn that project-scope MCP configs now carry the literal secret and must be gitignored.

Test Plan

• npx tsc --noEmit — clean
• npm run build — success
• npx vitest run — 1827 passed, 0 failed
• Rewrote the project-secret and codex tests to assert plaintext Bearer <token> in every tool; updated the "unresolvable var skips" comment.
• End-to-end (teamai pull in a real project): .mcp.json, .cursor/mcp.json, .codebuddy/mcp.json all contain resolved Bearer <token>, no ${} in any of them.
• Backend probe with the resolved token: POST /api/ai/mcp → HTTP 200.

🤖 Generated with Claude Code