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/handlers/api.go

@@ -84,7 +84,7 @@ func (h *Handlers) HandleAPILoginPOST() http.HandlerFunc {
 		decodeErr := json.NewDecoder(request.Body).Decode(&req)
 		if decodeErr != nil {
 			h.respondJSON(writer, request,
-				map[string]string{"error": "invalid JSON body"},
+				map[string]string{jsonKeyError: "invalid JSON body"},
 				http.StatusBadRequest)
 
 			return
@@ -95,7 +95,7 @@ func (h *Handlers) HandleAPILoginPOST() http.HandlerFunc {
 
 		if username == "" || credential == "" {
 			h.respondJSON(writer, request,
-				map[string]string{"error": "username and password are required"},
+				map[string]string{jsonKeyError: "username and password are required"},
 				http.StatusBadRequest)
 
 			return
@@ -104,7 +104,7 @@ func (h *Handlers) HandleAPILoginPOST() http.HandlerFunc {
 		user, authErr := h.auth.Authenticate(request.Context(), username, credential)
 		if authErr != nil {
 			h.respondJSON(writer, request,
-				map[string]string{"error": "invalid credentials"},
+				map[string]string{jsonKeyError: "invalid credentials"},
 				http.StatusUnauthorized)
 
 			return
@@ -114,7 +114,7 @@ func (h *Handlers) HandleAPILoginPOST() http.HandlerFunc {
 		if sessionErr != nil {
 			h.log.Error("api: failed to create session", "error", sessionErr)
 			h.respondJSON(writer, request,
-				map[string]string{"error": "failed to create session"},
+				map[string]string{jsonKeyError: "failed to create session"},
 				http.StatusInternalServerError)
 
 			return
@@ -133,7 +133,7 @@ func (h *Handlers) HandleAPIListApps() http.HandlerFunc {
 		apps, err := h.appService.ListApps(request.Context())
 		if err != nil {
 			h.respondJSON(writer, request,
-				map[string]string{"error": "failed to list apps"},
+				map[string]string{jsonKeyError: "failed to list apps"},
 				http.StatusInternalServerError)
 
 			return
@@ -156,7 +156,7 @@ func (h *Handlers) HandleAPIGetApp() http.HandlerFunc {
 		application, err := h.appService.GetApp(request.Context(), appID)
 		if err != nil {
 			h.respondJSON(writer, request,
-				map[string]string{"error": "internal server error"},
+				map[string]string{jsonKeyError: "internal server error"},
 				http.StatusInternalServerError)
 
 			return
@@ -164,7 +164,7 @@ func (h *Handlers) HandleAPIGetApp() http.HandlerFunc {
 
 		if application == nil {
 			h.respondJSON(writer, request,
-				map[string]string{"error": "app not found"},
+				map[string]string{jsonKeyError: "app not found"},
 				http.StatusNotFound)
 
 			return
@@ -185,7 +185,7 @@ func (h *Handlers) HandleAPIListDeployments() http.HandlerFunc {
 		application, err := h.appService.GetApp(request.Context(), appID)
 		if err != nil || application == nil {
 			h.respondJSON(writer, request,
-				map[string]string{"error": "app not found"},
+				map[string]string{jsonKeyError: "app not found"},
 				http.StatusNotFound)
 
 			return
@@ -205,7 +205,7 @@ func (h *Handlers) HandleAPIListDeployments() http.HandlerFunc {
 		)
 		if deployErr != nil {
 			h.respondJSON(writer, request,
-				map[string]string{"error": "failed to list deployments"},
+				map[string]string{jsonKeyError: "failed to list deployments"},
 				http.StatusInternalServerError)
 
 			return
@@ -231,7 +231,7 @@ func (h *Handlers) HandleAPIWhoAmI() http.HandlerFunc {
 		user, err := h.auth.GetCurrentUser(request.Context(), request)
 		if err != nil || user == nil {
 			h.respondJSON(writer, request,
-				map[string]string{"error": "unauthorized"},
+				map[string]string{jsonKeyError: "unauthorized"},
 				http.StatusUnauthorized)
 
 			return