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/examples/sdk/10-settings.ts

@@ -7,11 +7,11 @@
 import { createAgentSession, loadSettings, SessionManager, SettingsManager } from "@oh-my-pi/pi-coding-agent";
 
 // Load current settings (merged global + project)
-const settings = loadSettings();
+const settings = await loadSettings();
 console.log("Current settings:", JSON.stringify(settings, null, 2));
 
 // Override specific settings
-const settingsManager = SettingsManager.create();
+const settingsManager = await SettingsManager.create();
 settingsManager.applyOverrides({
 	compaction: { enabled: false },
 	retry: { enabled: true, maxRetries: 5, baseDelayMs: 1000 },