feat(co-browser): Register co-browser tools in MCP server

[coderooz]

Register co-browser tools in tools/index.js and mcp-server.js.

Acceptance criteria:

• Add co-browser tool handlers to tools/index.js toolHandlers map
• Add tool definitions to mcp-server.js getTools() array
• Add dispatch handlers in mcp-server.js tools/call if-chain
• Follow existing pattern (see browser tools registration)

Files to modify: tools/index.js, mcp-server.js

Depends on: co-browser tools (#47)
Milestone: v2.8.0