Add project-specific settings and SettingsManager factories

- SettingsManager now loads .pi/settings.json from cwd (project settings)
- Project settings merge with global settings (deep merge for objects)
- Setters only modify global settings, project settings are read-only
- Add static factories: SettingsManager.create(cwd?, agentDir?), SettingsManager.inMemory(settings?)
- Add applyOverrides() for programmatic overrides
- Replace 'settings' option with 'settingsManager' in CreateAgentSessionOptions
- Update examples to use new pattern

Incorporates PR #276 approach

packages/coding-agent/examples/sdk/10-settings.ts

@@ -1,33 +1,38 @@
 /**
  * Settings Configuration
  *
- * Override settings from agentDir/settings.json.
+ * Override settings using SettingsManager.
  */
 
-import { createAgentSession, loadSettings, SessionManager } from "../../src/index.js";
+import { createAgentSession, loadSettings, SessionManager, SettingsManager } from "../../src/index.js";
 
-// Load current settings
+// Load current settings (merged global + project)
 const settings = loadSettings();
 console.log("Current settings:", JSON.stringify(settings, null, 2));
 
 // Override specific settings
+const settingsManager = SettingsManager.create();
+settingsManager.applyOverrides({
+	compaction: { enabled: false },
+	retry: { enabled: true, maxRetries: 5, baseDelayMs: 1000 },
+});
+
 const { session } = await createAgentSession({
-	settings: {
-		// Disable auto-compaction
-		compaction: { enabled: false },
-
-		// Custom retry behavior
-		retry: {
-			enabled: true,
-			maxRetries: 5,
-			baseDelayMs: 1000,
-		},
-
-		// Terminal options
-		terminal: { showImages: true },
-		hideThinkingBlock: true,
-	},
+	settingsManager,
 	sessionManager: SessionManager.inMemory(),
 });
 
 console.log("Session created with custom settings");
+
+// For testing without file I/O:
+const inMemorySettings = SettingsManager.inMemory({
+	compaction: { enabled: false },
+	retry: { enabled: false },
+});
+
+const { session: testSession } = await createAgentSession({
+	settingsManager: inMemorySettings,
+	sessionManager: SessionManager.inMemory(),
+});
+
+console.log("Test session created with in-memory settings");