fix: use LLVM unstable repo for Debian trixie/forky

The LLVM apt repository (apt.llvm.org) doesn't have a dedicated release
for Debian trixie (13) or forky. When running llvm.sh on these distros,
it tries to access llvm-toolchain-trixie-19 which returns a 404.

This fix passes -n=unstable to llvm.sh when running on Debian trixie or
forky, directing it to use the unstable repository which does have the
packages available.

Fixes the docker image build failure:
E: The repository 'http://apt.llvm.org/trixie llvm-toolchain-trixie-19 Release' does not have a Release file.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: Claude Bot

scripts/bootstrap.sh

@@ -1157,7 +1157,18 @@ install_llvm() {
 	apt)
 		bash="$(require bash)"
 		llvm_script="$(download_file "https://apt.llvm.org/llvm.sh")"
-		execute_sudo "$bash" "$llvm_script" "$(llvm_version)" all
+
+		# Debian trixie and newer don't have their own LLVM apt repo, use unstable
+		llvm_codename_arg=""
+		if [ "$distro" = "debian" ]; then
+			case "$VERSION_CODENAME" in
+			trixie|forky)
+				llvm_codename_arg="-n=unstable"
+				;;
+			esac
+		fi
+
+		execute_sudo "$bash" "$llvm_script" "$(llvm_version)" all $llvm_codename_arg
 
 		# Install llvm-symbolizer explicitly to ensure it's available for ASAN
 		install_packages "llvm-$(llvm_version)-tools"