Read skills from the global and workspace .agents/skills directories

- Discover skill directories under ~/.agents/skills and each
  workspace''s .agents/skills; a directory qualifies with a full
  skill.manifest.json or just a SKILL.md, whose manifest is derived
  (frontmatter name or the directory name). Paths resolve per platform
  on Windows, macOS, and Linux.
- Sync at startup for every organization and again when the Skills
  page opens; skills the org already carries are skipped, and one
  broken directory cannot block the rest.
- AGENTCOMPANY_NEW_SKILLS_ROOT points tests at a temporary library
  (overriding USERPROFILE crashes Electron on Windows).

src/shared/desktop-api.ts

@@ -61,6 +61,7 @@ import type {
   RunSdlcReviewInput,
   RunSkillTestsInput,
   RunTaskInput,
+  SyncSkillsFromDiskInput,
   RevokeProviderCredentialInput,
   SaveProviderCredentialInput,
   ComposioToolkitSummaryDto,
@@ -152,6 +153,7 @@ export interface DesktopApi {
   streamProviderResponse(input: StreamProviderResponseInput): Promise<DesktopResult<AppSnapshot>>;
   cancelProviderResponse(input: CancelProviderResponseInput): Promise<DesktopResult<AppSnapshot>>;
   importSkillDirectory(input: ImportSkillDirectoryInput): Promise<DesktopResult<AppSnapshot>>;
+  syncSkillsFromDisk(input: SyncSkillsFromDiskInput): Promise<DesktopResult<AppSnapshot>>;
   bindSkill(input: BindSkillInput): Promise<DesktopResult<AppSnapshot>>;
   resolveAgentSkills(input: ResolveAgentSkillsInput): Promise<DesktopResult<AppSnapshot>>;
   runSkillTests(input: RunSkillTestsInput): Promise<DesktopResult<AppSnapshot>>;