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/main/services/skill-manifest.ts

@@ -16,12 +16,12 @@ export interface SkillManifest {
   outputs: unknown;
 }
 
-export function loadSkillManifest(directoryPath: string, requestedVersion: string): SkillManifest {
+export function loadSkillManifest(directoryPath: string, requestedVersion?: string): SkillManifest {
   const manifestPath = join(directoryPath, "skill.manifest.json");
   if (!existsSync(manifestPath)) throw new Error("skill.manifest.json is required.");
   const raw = JSON.parse(readFileSync(manifestPath, "utf8")) as Record<string, unknown>;
   const manifest = normalizeManifest(raw);
-  if (manifest.version !== requestedVersion) {
+  if (requestedVersion !== undefined && manifest.version !== requestedVersion) {
     throw new Error("Skill manifest version must match the requested version.");
   }
   verifyDeclaredFile(directoryPath, manifest.entrypoint);