feat(skills): GitHub PAT support for private skill repos

- Add optional authToken to skill import for GitHub private repos
- Store PAT as encrypted company secret (skill-pat:{skillId})
- Thread auth token through ghFetch and GitHub resolution helpers
- Add PATCH /companies/:companyId/skills/:skillId/auth for managing PAT per skill
- Preserve sourceAuthSecretId across skill re-imports/updates
- Delete PAT secret on PAT clear and on skill deletion to prevent orphans
- UI: Add PAT input field in import form for GitHub URLs
- UI: Add SkillAuthSection with ShieldCheck icon for viewing/updating/removing PAT

packages/shared/src/validators/index.ts

@@ -63,6 +63,7 @@ export {
   companySkillDetailSchema,
   companySkillUpdateStatusSchema,
   companySkillImportSchema,
+  companySkillUpdateAuthSchema,
   companySkillProjectScanRequestSchema,
   companySkillProjectScanSkippedSchema,
   companySkillProjectScanConflictSchema,
@@ -74,6 +75,7 @@ export {
   type CompanySkillProjectScan,
   type CompanySkillCreate,
   type CompanySkillFileUpdate,
+  type CompanySkillUpdateAuth,
 } from "./company-skill.js";
 export {
   agentSkillStateSchema,