fix: make Agent updates reliable and visible

Valid Agent packages could be rejected when packaged trusted-key JSON used CRLF, and Settings could not show whether a newer compatible Agent existed. Registry formatting is now parsed independently of cryptographic trust, and Settings reads only the signed catalog to report local and latest versions.

New installations use a credential-free local Ollama-compatible profile. The v20 migration changes only untouched historical defaults, while explicit profiles and legacy environment aliases remain compatible. Magic Notes count badges no longer shift navigation rows.

Release note: 修复 Agent 下载兼容性并在设置中显示更新状态；新安装默认连接本地模型，保留显式用户配置；魔法笔记待办数字不再改变侧栏菜单高度。

src/shared/agent-package-contracts.test.ts

@@ -67,12 +67,19 @@ describe('Agent package contracts', () => {
       platform: 'linux',
       state: 'not-downloaded',
       version: null,
+      latestVersion: null,
+      updateAvailable: false,
       remoteRuntimeVersion: null,
       agentProtocol: null
     } as const
     expect(
       agentPackageInventorySchema.parse({
         checkedAt: '2026-08-25T00:00:00.000Z',
+        catalog: {
+          state: 'not-checked',
+          checkedAt: null,
+          error: null
+        },
         entries: [
           { ...entry, architecture: 'x64' },
           { ...entry, architecture: 'arm64' }
@@ -82,6 +89,11 @@ describe('Agent package contracts', () => {
     expect(() =>
       agentPackageInventorySchema.parse({
         checkedAt: '2026-08-25T00:00:00.000Z',
+        catalog: {
+          state: 'not-checked',
+          checkedAt: null,
+          error: null
+        },
         entries: [
           { ...entry, architecture: 'x64' },
           { ...entry, architecture: 'x64' }