Add integration test coverage for new server architecture

[smartlabsAT]

TL;DR: Add an automated integration test that exercises the new server architecture end-to-end via MCP protocol.

Context

Part of Epic #35 (v0.2.0 architecture cleanup). After #39 introduces the layered architecture, an integration test verifies the full chain: client connects via stdio → tool listing → tool execution → clean shutdown. The test uses the user-facing entry point (dist/mcp/server.cjs shim) to also verify backward compatibility.

Acceptance Criteria

• New test file tests/integration/proxy-server.test.js covers server start, tool listing, tool execution, and clean shutdown
• New npm script test:integration runs the test (separate from npm test to keep dev loop fast)
• CI skip guard if Chromium not available (exit 0, not failure)

Scope

In Scope:

• Create tests/integration/proxy-server.test.js using hand-rolled Node.js assertions (project convention — no test framework installed)
• Add test:integration script to package.json
• Chromium availability check with graceful skip
• Test via dist/mcp/server.cjs (the shim path, verifying backward compat)

Out of Scope:

• Test framework adoption (Jest, Vitest, etc.)
• Testing of local tools (none registered in Epic 1)
• Performance benchmarks (deferred to Epic 2)

Technical Implementation

• Test structure (CJS, matches project convention):
  • Spawn server via StdioClientTransport pointing at dist/mcp/server.cjs
  • Connect with Client from @modelcontextprotocol/sdk/client/index.js (already installed, v1.17.4)
  • Assert tools/list returns ≥ 20 tools (lower bound allows minor upstream version drift; PoC confirmed 23)
  • Execute browser_navigate to about:blank, browser_snapshot, browser_close
  • Verify clean client disconnect
• Pre-flight: Check Chromium availability; skip test with exit 0 if not installed
• Prerequisite: npm run build must run before test:integration (tests the built artifact)
• Directory: tests/integration/ exists (currently empty)

Architecture Reference

From Epic #35 Architecture Decisions:

• Test uses the backward-compat shim path (dist/mcp/server.cjs) to verify .mcp.json compatibility

Dependencies

• Blocked by: Modularize MCP server into routing and execution layers #39 (tests the architecture introduced by Modularize MCP server into routing and execution layers #39)
• Required for: Release v0.2.0-alpha.1 #41 (release)