M2: the four V1 atoms + Git sync (Gitea / filesystem)

- Author the four V1 skill atoms in skills/ (Git is the source of truth): spec-writing &
  story-breakdown (product-owner), test-plan-generation & diff-review (qa) — each with
  risk-tagged actions, golden tests, and a body.
- SharedKernel: IGitProvider seam (read-only, provider-agnostic) + GitFile.
- Integrations module (its first real code): FileSystemGitProvider (dogfood/local) and a
  GiteaGitProvider (Gitea REST: recursive tree → SKILL.md blobs → base64 contents); the
  provider is chosen by GitSource:Provider config.
- Skills: SkillSyncService consumes IGitProvider (never Integrations) and indexes each file;
  POST /api/skills/sync and a POST /api/skills/webhook/gitea (re-sync on push; signature
  verification + changed-file-only + queue offload come later).

Verified: build green; ArchitectureTests 8/8 (Skills & Integrations reference only
SharedKernel; the Git seam lives in SharedKernel); IntegrationTests 22/22 incl. a sync that
indexes the four real atoms from skills/, published and queryable by role.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Modules/TeamUp.Modules.Skills/Endpoints/SkillsEndpoints.cs

@@ -5,6 +5,7 @@ using Microsoft.EntityFrameworkCore;
 using TeamUp.Modules.Skills.Domain;
 using TeamUp.Modules.Skills.Indexing;
 using TeamUp.Modules.Skills.Persistence;
+using TeamUp.Modules.Skills.Sync;
 using TeamUp.SharedKernel.Modularity;
 
 namespace TeamUp.Modules.Skills.Endpoints;
@@ -19,8 +20,18 @@ internal static class SkillsEndpoints
         group.MapGet("/", ListSkills).RequireAuthorization();
         group.MapGet("/{key}", GetSkill).RequireAuthorization();
         group.MapPost("/index", IndexSkill).RequireAuthorization();
+        group.MapPost("/sync", Sync).RequireAuthorization();
+        group.MapPost("/webhook/gitea", Webhook).AllowAnonymous();
     }
 
+    private static async Task<IResult> Sync(SkillSyncService sync, CancellationToken ct) =>
+        Results.Ok(new SyncResult(await sync.SyncAsync(ct)));
+
+    // Gitea push webhook → re-sync the source. M2 re-indexes the whole source (idempotent);
+    // signature verification + changed-file-only sync via the job queue land later.
+    private static async Task<IResult> Webhook(SkillSyncService sync, CancellationToken ct) =>
+        Results.Ok(new SyncResult(await sync.SyncAsync(ct)));
+
     private static async Task<IResult> ListSkills(
         string? role, string? visibility, SkillsDbContext db, CancellationToken ct)
     {