Update golangci-lint to v2.12.2 with canonical config

Bump golangci-lint from v2.10.1 to v2.12.2 in the Dockerfile lint
stage (tag+digest pin) and script/bootstrap release-archive pins
(linux amd64/arm64 sha256s). Replace .golangci.yml with the canonical
v2-layout config so linter settings (lll 88, funlen 80/50, cyclop 15,
dupl 100) actually apply.

Fix all findings surfaced by the new linter and config:

- noctx: use httptest.NewRequestWithContext in all tests
- gosec G710/G703: route app redirects through a path-escaping
  redirectToApp helper; annotate internal log path usage
- goconst: introduce shared constants for template/JSON keys and
  repeated test literals
- lll: wrap lines to the 88-column limit
- dupl: extract shared helpers (generic findAllByAppID in models,
  deleteAppResource in handlers, parsePush in webhook payloads,
  table-driven/helper-based test dedup)
- nolintlint: drop nolint directives made obsolete by the new limits

Record the change in TODO.md; make check is green.

internal/handlers/repo_url_validation_test.go

@@ -22,7 +22,11 @@ func TestValidateRepoURL(t *testing.T) {
 		{name: "SCP-like URL", url: "git@github.com:user/repo.git", wantErr: false},
 		{name: "SCP-like with dots", url: "git@git.example.com:org/repo.git", wantErr: false},
 		{name: "https without .git", url: "https://github.com/user/repo", wantErr: false},
-		{name: "https with port", url: "https://git.example.com:8443/user/repo.git", wantErr: false},
+		{
+			name:    "https with port",
+			url:     "https://git.example.com:8443/user/repo.git",
+			wantErr: false,
+		},
 
 		// Invalid URLs
 		{name: "empty string", url: "", wantErr: true},
@@ -37,10 +41,22 @@ func TestValidateRepoURL(t *testing.T) {
 		{name: "no path https", url: "https://github.com", wantErr: true},
 		{name: "no path https trailing slash", url: "https://github.com/", wantErr: true},
 		{name: "SCP-like non-git user", url: "root@github.com:user/repo.git", wantErr: true},
-		{name: "SCP-like arbitrary user", url: "admin@github.com:user/repo.git", wantErr: true},
+		{
+			name:    "SCP-like arbitrary user",
+			url:     "admin@github.com:user/repo.git",
+			wantErr: true,
+		},
 		{name: "path traversal SCP", url: "git@github.com:../../etc/passwd", wantErr: true},
-		{name: "path traversal https", url: "https://github.com/user/../../../etc/passwd", wantErr: true},
-		{name: "path traversal in middle", url: "https://github.com/user/repo/../secret", wantErr: true},
+		{
+			name:    "path traversal https",
+			url:     "https://github.com/user/../../../etc/passwd",
+			wantErr: true,
+		},
+		{
+			name:    "path traversal in middle",
+			url:     "https://github.com/user/repo/../secret",
+			wantErr: true,
+		},
 	}
 
 	for _, tc := range tests {