feat(coding-agent): converted capability loading and discovery providers to async APIs with caching fs layer

- Converted SettingsManager.create(), loadSettings(), discoverSkills(), loadSlashCommands(), buildSystemPrompt(), loadSkills(), loadProjectContextFiles(), and getShellConfig() from synchronous to asynchronous APIs.
- Changed capability provider load() method from supporting both sync and async to async-only by removing loadSync().
- Removed fs property from LoadContext interface in capability types.
- Added new fs.ts module with caching layer for filesystem operations using readFile, readDirEntries, readDir, walkUp, and cache management functions.
- Refactored all discovery providers (builtin, claude, cline, codex, cursor, gemini, github, mcp-json, ssh, vscode, windsurf) to use async file operations with Promise.all for parallel loading.

packages/coding-agent/test/utilities.ts

@@ -100,7 +100,7 @@ export async function createTestSession(options: TestSessionOptions = {}): Promi
 	});
 
 	const sessionManager = options.inMemory ? SessionManager.inMemory() : SessionManager.create(tempDir);
-	const settingsManager = SettingsManager.create(tempDir, tempDir);
+	const settingsManager = await SettingsManager.create(tempDir, tempDir);
 
 	if (options.settingsOverrides) {
 		settingsManager.applyOverrides(options.settingsOverrides);