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/database/migrations.go

@@ -32,7 +32,10 @@ var ErrInvalidMigrationFilename = errors.New("invalid migration filename")
 func ParseMigrationVersion(filename string) (int, error) {
 	name := strings.TrimSuffix(filename, ".sql")
 	if name == "" || name == filename {
-		return 0, fmt.Errorf("%w: %q has no .sql extension or is empty", ErrInvalidMigrationFilename, filename)
+		return 0, fmt.Errorf(
+			"%w: %q has no .sql extension or is empty",
+			ErrInvalidMigrationFilename, filename,
+		)
 	}
 
 	// Split on underscore to separate version from description.
@@ -40,7 +43,10 @@ func ParseMigrationVersion(filename string) (int, error) {
 	versionStr, _, _ := strings.Cut(name, "_")
 
 	if versionStr == "" {
-		return 0, fmt.Errorf("%w: %q has empty version prefix", ErrInvalidMigrationFilename, filename)
+		return 0, fmt.Errorf(
+			"%w: %q has empty version prefix",
+			ErrInvalidMigrationFilename, filename,
+		)
 	}
 
 	// Validate the version is purely numeric.
@@ -177,7 +183,12 @@ func ApplyMigrations(ctx context.Context, db *sql.DB, log *slog.Logger) error {
 
 // applyMigrationTx reads and executes a migration file within a transaction,
 // recording the version in schema_migrations on success.
-func applyMigrationTx(ctx context.Context, db *sql.DB, filename string, version int) error {
+func applyMigrationTx(
+	ctx context.Context,
+	db *sql.DB,
+	filename string,
+	version int,
+) error {
 	content, err := migrationsFS.ReadFile("migrations/" + filename)
 	if err != nil {
 		return fmt.Errorf("failed to read migration %s: %w", filename, err)