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>

tests/TeamUp.IntegrationTests/TeamUpWebFactory.cs

@@ -7,7 +7,9 @@ namespace TeamUp.IntegrationTests;
 /// Drives the real <see cref="Program"/> web host against the test container, in Development so
 /// migrations apply on startup and the OpenAPI document is mapped.
 /// </summary>
-public sealed class TeamUpWebFactory(string connectionString) : WebApplicationFactory<Program>
+public sealed class TeamUpWebFactory(
+    string connectionString,
+    IReadOnlyDictionary<string, string?>? settings = null) : WebApplicationFactory<Program>
 {
     protected override void ConfigureWebHost(IWebHostBuilder builder)
     {
@@ -15,5 +17,13 @@ public sealed class TeamUpWebFactory(string connectionString) : WebApplicationFa
         builder.UseSetting("ConnectionStrings:Postgres", connectionString);
         builder.UseSetting("Database:ApplyMigrationsOnStartup", "true");
         builder.UseSetting("OpenTelemetry:OtlpEndpoint", string.Empty);
+
+        if (settings is not null)
+        {
+            foreach (var (key, value) in settings)
+            {
+                builder.UseSetting(key, value);
+            }
+        }
     }
 }