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/shared/contracts/ipc.ts

@@ -70,6 +70,23 @@ export interface SaveLspProfileInput {
   profile: LspProfileDefinition;
 }
 
+export type DiscoveredToolingResolution = 'accept' | 'dismiss';
+
+export interface RescanProjectConfigsInput {
+  projectId: string;
+}
+
+export interface ResolveProjectDiscoveredToolingInput {
+  projectId: string;
+  serverIds: string[];
+  resolution: DiscoveredToolingResolution;
+}
+
+export interface ResolveWorkspaceDiscoveredToolingInput {
+  serverIds: string[];
+  resolution: DiscoveredToolingResolution;
+}
+
 export interface UpdateSessionToolingInput extends SessionToolingSelection {
   sessionId: string;
 }
@@ -85,7 +102,10 @@ export interface ElectronApi {
   loadWorkspace(): Promise<WorkspaceState>;
   addProject(): Promise<WorkspaceState>;
   removeProject(projectId: string): Promise<WorkspaceState>;
+  resolveWorkspaceDiscoveredTooling(input: ResolveWorkspaceDiscoveredToolingInput): Promise<WorkspaceState>;
   refreshProjectGitContext(projectId?: string): Promise<WorkspaceState>;
+  rescanProjectConfigs(input: RescanProjectConfigsInput): Promise<WorkspaceState>;
+  resolveProjectDiscoveredTooling(input: ResolveProjectDiscoveredToolingInput): Promise<WorkspaceState>;
   savePattern(input: SavePatternInput): Promise<WorkspaceState>;
   deletePattern(patternId: string): Promise<WorkspaceState>;
   saveMcpServer(input: SaveMcpServerInput): Promise<WorkspaceState>;