added .claude/skills: introduced on-demand skill guides for architecture, PR documentation, and testing conventions; updated AGENTS.md to reference new skills

.claude/skills/writing-tests/SKILL.md

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+---
+name: writing-tests
+description: GitTally testing conventions — Kotest FunSpec spec structure, MockK matchers, and the two patterns for mocking beans in Spring slice tests (springmockk @MockkBean or @TestConfiguration). Use when writing, extending, or refactoring tests.
+---
+
+# Writing Tests for GitTally
+
+Tests use **Kotest `FunSpec`** style. `SpringExtension` is registered globally in `io.kotest.provided.ProjectConfig` — do not add it per-spec.
+
+```kotlin
+class MyTest : FunSpec() {
+    init {
+        test("description") { ... }
+        beforeEach { ... }
+    }
+}
+```
+
+Use `shouldBe`, `shouldNotBe`, `shouldThrow` etc. from `io.kotest.matchers`.
+
+Tests mirror the production package structure under `src/test/kotlin`.
+
+Run a single test class instead of the full suite while iterating:
+
+```bash
+./gradlew test --tests "de.hoennig.gittally.ApplicationContextTest"
+```
+
+## Mocking in Spring Slice Tests
+
+Use `@MockkBean` from `springmockk` to inject MockK mocks into the Spring context:
+
+```kotlin
+@WebMvcTest(SomeController::class)
+class SomeControllerTest : FunSpec() {
+    @MockkBean
+    lateinit var someService: SomeService
+    init {
+        beforeEach { clearMocks(someService) }
+        // full MockK syntax: every { } / verify { }
+    }
+}
+```
+
+Alternatively, register mocks via `@TestConfiguration` without the springmockk dependency:
+
+```kotlin
+@WebMvcTest(SomeController::class)
+@Import(SomeControllerTest.Mocks::class)
+class SomeControllerTest : FunSpec() {
+    @TestConfiguration
+    class Mocks {
+        @Bean fun someService(): SomeService = mockk()
+    }
+    @Autowired lateinit var someService: SomeService
+    init {
+        beforeEach { clearMocks(someService) }
+    }
+}
+```
+
+Pure unit tests (no Spring context) use MockK directly without any Spring wiring.
+
+## Test Infrastructure by Layer
+
+- Git-facing code: integration tests against local fixture repositories (bare origin + clones), see `GitServiceTest` — no network access, hermetic git environment variables.
+- HTTP clients (Gitea): WireMock.
+- Docker-dependent code: Testcontainers.
+- The `Watcher` and other schedulers never start their loops in tests; call `poll()`/lifecycle methods directly.