feat: auto-discover MCP servers from project and user config files

Scan .vscode/mcp.json, .mcp.json, .copilot/mcp.json (project-level) and
~/.copilot/mcp.json (user-level) for MCP server definitions. Discovered
servers require explicit user acceptance before activation.

Backend:
- Add ConfigScannerRegistry with per-format scanners and  substitution
- Add discovered tooling domain model with fingerprint-based change detection
- Integrate scanning into workspace load, project add, and project selection
- Merge accepted discovered MCPs into effective runtime tooling
- Extend sidecar contracts with env/headers for real-world MCP configs
- Add IPC channels for accept/dismiss/rescan operations

Frontend:
- Add DiscoveredToolingModal for reviewing pending MCP servers
- Auto-show modal when pending discoveries exist on load or project switch
- Add amber badge on sidebar project headers for pending discoveries
- Add discovered MCP section in Settings panel with accept/dismiss/rescan
- Group InlinePills tool dropdown by Workspace MCP / User MCP / Project MCP
- Pass effective project tooling (including accepted discoveries) to ChatPane

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/preload/index.ts

@@ -9,7 +9,12 @@ const api: ElectronApi = {
   loadWorkspace: () => ipcRenderer.invoke(ipcChannels.loadWorkspace),
   addProject: () => ipcRenderer.invoke(ipcChannels.addProject),
   removeProject: (projectId) => ipcRenderer.invoke(ipcChannels.removeProject, projectId),
+  resolveWorkspaceDiscoveredTooling: (input) =>
+    ipcRenderer.invoke(ipcChannels.resolveWorkspaceDiscoveredTooling, input),
   refreshProjectGitContext: (projectId) => ipcRenderer.invoke(ipcChannels.refreshProjectGitContext, projectId),
+  rescanProjectConfigs: (input) => ipcRenderer.invoke(ipcChannels.rescanProjectConfigs, input),
+  resolveProjectDiscoveredTooling: (input) =>
+    ipcRenderer.invoke(ipcChannels.resolveProjectDiscoveredTooling, input),
   savePattern: (input) => ipcRenderer.invoke(ipcChannels.savePattern, input),
   deletePattern: (patternId) => ipcRenderer.invoke(ipcChannels.deletePattern, patternId),
   setPatternFavorite: (input) => ipcRenderer.invoke(ipcChannels.setPatternFavorite, input),