Update golangci-lint to v2.12.2 with canonical config (#187)

Bumps golangci-lint from v2.10.1 to v2.12.2 everywhere it is pinned and installs the canonical `.golangci.yml`, then fixes every finding the new linter surfaces so `make check` is green.

## Version pins

- `Dockerfile` lint stage: `golangci/golangci-lint:v2.12.2` (Debian-based), tag plus digest pin
- `script/bootstrap`: `GOLANGCI_LINT_VERSION=2.12.2` with updated `linux-amd64`/`linux-arm64` release-archive sha256 pins

## Config

`.golangci.yml` replaced with the canonical config. Material change: the old file declared `version: "2"` but kept settings under the legacy top-level `linters-settings` key, which golangci-lint v2 ignores — so the intended thresholds (`lll` 88, `funlen` 80/50, `cyclop` 15, `dupl` 100) were not being applied. The canonical file moves them under `linters.settings` and drops `issues.exclude-use-default`.

## Lint fixes (216 findings)

- `lll` (96): wrapped lines to the 88-column limit
- `noctx` (46): `httptest.NewRequestWithContext` with `t.Context()` throughout the tests
- `goconst` (24): shared constants for template/JSON keys in `internal/handlers` and repeated test literals
- `gosec` (23): app-page redirects now go through a `redirectToApp` helper that path-escapes the app ID (G710 open redirect); `http.ServeFile` of the internally derived deployment log path annotated like the adjacent `os.Stat` (G703)
- `dupl` (22): extracted a generic `findAllByAppID` in `internal/models`, a `deleteAppResource` helper in `internal/handlers`, a shared `parsePush` in `internal/service/webhook`, and table-driven/helper-based dedup in tests
- `nolintlint` (5): removed `//nolint:funlen` directives made obsolete by the new limits (plus one more that became obsolete after refactoring)
- `nilerr` (3, surfaced during fixing): resource-delete lookups now propagate the find error to the caller

No behavior changes intended; all tests pass and `make check` is green.

Note: golangci-lint v2.12 warns that `gomodguard` is deprecated in favor of `gomodguard_v2` — a future canonical-config update should address this centrally.
Co-authored-by: sneak <sneak@sneak.berlin>
Reviewed-on: #187
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

internal/service/auth/auth_test.go

@@ -121,7 +121,7 @@ func getSessionCookie(t *testing.T, svc *auth.Service) *http.Cookie {
 	require.NoError(t, err)
 
 	recorder := httptest.NewRecorder()
-	request := httptest.NewRequest(http.MethodGet, "/", nil)
+	request := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", nil)
 
 	err = svc.CreateSession(recorder, request, user)
 	require.NoError(t, err)
@@ -144,7 +144,11 @@ func TestSessionCookieSecureFlag(testingT *testing.T) {
 		svc := setupAuthService(t, false)
 		cookie := getSessionCookie(t, svc)
 		require.NotNil(t, cookie, "session cookie should exist")
-		assert.True(t, cookie.Secure, "session cookie should have Secure flag in production mode")
+		assert.True(
+			t,
+			cookie.Secure,
+			"session cookie should have Secure flag in production mode",
+		)
 	})
 }
 
@@ -324,7 +328,12 @@ func TestCreateUserRaceCondition(testingT *testing.T) {
 		}
 
 		assert.Equal(t, 1, successes, "exactly one goroutine should succeed")
-		assert.Equal(t, goroutines-1, failures, "all other goroutines should fail with ErrUserExists")
+		assert.Equal(
+			t,
+			goroutines-1,
+			failures,
+			"all other goroutines should fail with ErrUserExists",
+		)
 	})
 }
 
@@ -380,7 +389,9 @@ func TestDestroySessionMaxAge(testingT *testing.T) {
 		defer cleanup()
 
 		recorder := httptest.NewRecorder()
-		request := httptest.NewRequest(http.MethodGet, "/", nil)
+		request := httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, "/", nil,
+		)
 
 		err := svc.DestroySession(recorder, request)
 		require.NoError(t, err)