fix(mcp): derive default version from package metadata

[wuyua9]

Summary

• derive the default MCP server version from packages/mcp/package.json instead of the stale hard-coded 1.0.0
• preserve the MCP_SERVER_VERSION environment override
• add focused regression coverage for the package default and override paths

Why

createMcpConfig() passes config.version into the MCP server metadata. The package is currently versioned as 0.1.13, but a default install still reports 1.0.0 unless MCP_SERVER_VERSION is set.

Tests

• ./node_modules/.bin/tsc --build packages/core --force
• cd packages/mcp && node --import tsx --test "src/config.test.ts"
• ./node_modules/.bin/tsc --build packages/mcp --force
• git diff --check

Note: pnpm --filter @zilliz/claude-context-mcp test -- --test-name-pattern 'server version' attempted to run through the local pnpm shim, but pnpm 11 aborted with ERR_PNPM_ABORTED_REMOVE_MODULES_DIR_NO_TTY before executing tests, so I used the package's underlying node --import tsx --test command directly.