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/main/persistence/workspaceRepository.ts

@@ -3,6 +3,7 @@ import { mkdir } from 'node:fs/promises';
 import { createBuiltinPatterns, resolvePatternGraph } from '@shared/domain/pattern';
 import type { PatternDefinition } from '@shared/domain/pattern';
 import { mergeScratchpadProject } from '@shared/domain/project';
+import { normalizeDiscoveredToolingState } from '@shared/domain/discoveredTooling';
 import { normalizeSessionRunRecords } from '@shared/domain/runTimeline';
 import {
   normalizeSessionToolingSelection,
@@ -63,7 +64,13 @@ export class WorkspaceRepository {
       return seeded;
     }
 
-    const projects = mergeScratchpadProject(stored.projects ?? [], this.scratchpadPath);
+    const projects = mergeScratchpadProject(
+      (stored.projects ?? []).map((project) => ({
+        ...project,
+        discoveredTooling: normalizeDiscoveredToolingState(project.discoveredTooling),
+      })),
+      this.scratchpadPath,
+    );
     const settings = normalizeWorkspaceSettings(stored.settings);
 
     const workspace: WorkspaceState = {