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/repo_url_validation.go

@@ -11,13 +11,17 @@ import (
 var (
 	errRepoURLEmpty   = errors.New("repository URL must not be empty")
 	errRepoURLScheme  = errors.New("file:// URLs are not allowed for security reasons")
-	errRepoURLInvalid = errors.New("repository URL must use https://, http://, ssh://, git://, or git@host:path format")
-	errRepoURLNoHost  = errors.New("repository URL must include a host")
-	errRepoURLNoPath  = errors.New("repository URL must include a path")
+	errRepoURLInvalid = errors.New(
+		"repository URL must use https://, http://, ssh://, git://, " +
+			"or git@host:path format",
+	)
+	errRepoURLNoHost = errors.New("repository URL must include a host")
+	errRepoURLNoPath = errors.New("repository URL must include a path")
 )
 
-// scpLikeRepoRe matches SCP-like git URLs: git@host:path (e.g. git@github.com:user/repo.git).
-// Only the "git" user is allowed, as that is the standard for SSH deploy keys.
+// scpLikeRepoRe matches SCP-like git URLs: git@host:path
+// (e.g. git@github.com:user/repo.git). Only the "git" user is allowed,
+// as that is the standard for SSH deploy keys.
 var scpLikeRepoRe = regexp.MustCompile(`^git@[a-zA-Z0-9._-]+:.+$`)
 
 // allowedRepoSchemes lists the URL schemes accepted for repository URLs.
@@ -30,7 +34,8 @@ var allowedRepoSchemes = map[string]bool{
 	"git":   true,
 }
 
-// validateRepoURL checks that the given repository URL is valid and uses an allowed scheme.
+// validateRepoURL checks that the given repository URL is valid and
+// uses an allowed scheme.
 func validateRepoURL(repoURL string) error {
 	if strings.TrimSpace(repoURL) == "" {
 		return errRepoURLEmpty