feat(coding-agent): refactored settings system with new singleton API and unified schema

- Replaced SettingsManager class with new Settings singleton providing synchronous get/set API and background persistence.
- Introduced settings-schema.ts as single source of truth for all configuration definitions with 100+ settings organized into logical groups.
- Migrated from method-based settings access (getTheme(), setTheme()) to path-based access using dot notation (settings.get('theme'), settings.set('theme', value)).
- Removed 2035-line settings-manager.ts file and replaced with modular settings.ts (693 lines) and settings-schema.ts (836 lines) for improved maintainability.
- Unified settings schema into single source of truth eliminating duplicate definitions across settings-defs.ts and settings-manager.ts.

packages/coding-agent/test/tools/python-execution.test.ts

@@ -1,4 +1,5 @@
 import { describe, expect, it, vi } from "bun:test";
+import { Settings } from "@oh-my-pi/pi-coding-agent/config/settings";
 import * as pythonExecutor from "@oh-my-pi/pi-coding-agent/ipy/executor";
 import type { ToolSession } from "@oh-my-pi/pi-coding-agent/tools";
 import { PythonTool } from "@oh-my-pi/pi-coding-agent/tools/python";
@@ -10,18 +11,12 @@ function createSession(cwd: string): ToolSession {
 		hasUI: false,
 		getSessionFile: () => "session-file",
 		getSessionSpawns: () => "*",
-		settings: {
-			getImageAutoResize: () => true,
-			getLspFormatOnWrite: () => true,
-			getLspDiagnosticsOnWrite: () => true,
-			getLspDiagnosticsOnEdit: () => false,
-			getEditFuzzyMatch: () => true,
-			getBashInterceptorEnabled: () => true,
-			getBashInterceptorSimpleLsEnabled: () => true,
-			getBashInterceptorRules: () => [],
-			getPythonToolMode: () => "ipy-only",
-			getPythonKernelMode: () => "per-call",
-		},
+		settings: Settings.isolated({
+			"lsp.formatOnWrite": true,
+			"bashInterceptor.enabled": true,
+			"python.toolMode": "ipy-only",
+			"python.kernelMode": "per-call",
+		}),
 	};
 }