feat: GenUI MCP service and Workspace coordination

GenUI Service (crates/goose-mcp/src/genui_service/ — 534 lines):
- MCP server for generating UI components via LLM
- Supports HTML/CSS/JS generation with structured output
- KPI display, chart generation, data table rendering
- Template-based component generation

Workspace Coordination (crates/goose/src/execution/workspace.rs — 532 lines):
- WorkspaceEventBus: broadcast channel for file/build/agent events
- FileLockManager: advisory soft-locking for multi-agent file access
- SharedWorkspace: combines event bus + file locks
- WorkspaceEvent enum: FileChanged, BuildStarted, BuildCompleted, etc.
- 16 unit tests

Cherry-picked from feature/cli-via-goosed with zero adaptation needed.

Signed-off-by: Jonathan MERCIER <bioinfornatics@gmail.com>

Author: bioinfornatics