refactor: consolidate utility functions into shared package

Move duplicate isObject, asString, asNumber, and safeStringify functions from multiple modules into a centralized shared/src/utils.ts module and update imports across cli, server, and web packages. This eliminates code duplication and improves maintainability.

shared/src/index.ts

@@ -1,4 +1,5 @@
 export * from './messages'
 export * from './modes'
 export * from './sessionSummary'
+export * from './utils'
 export type * from './types'

shared/src/messages.ts

@@ -1,13 +1,11 @@
+import { isObject } from './utils'
+
 type RoleWrappedRecord = {
     role: string
     content: unknown
     meta?: unknown
 }
 
-function isObject(value: unknown): value is Record<string, unknown> {
-    return Boolean(value) && typeof value === 'object'
-}
-
 export function isRoleWrappedRecord(value: unknown): value is RoleWrappedRecord {
     if (!isObject(value)) return false
     return typeof value.role === 'string' && 'content' in value

shared/src/utils.ts

@@ -0,0 +1,21 @@
+export function isObject(value: unknown): value is Record<string, unknown> {
+    return Boolean(value) && typeof value === 'object'
+}
+
+export function asString(value: unknown): string | null {
+    return typeof value === 'string' ? value : null
+}
+
+export function asNumber(value: unknown): number | null {
+    return typeof value === 'number' && Number.isFinite(value) ? value : null
+}
+
+export function safeStringify(value: unknown): string {
+    if (typeof value === 'string') return value
+    try {
+        const stringified = JSON.stringify(value, null, 2)
+        return typeof stringified === 'string' ? stringified : String(value)
+    } catch {
+        return String(value)
+    }
+}