Fix NVIDIA Kepler Logic & Kernel Headers

- Normalized PCI ID case sensitivity in `_helpers.sh`. The `detect_nvidia_arch()` function now converts input to uppercase (`${1^^}`) to match legacy architecture map keys, resolving "unknown" detection for all NVIDIA GPUs.
- Removed silent fallback to standard drivers in `gpu.sh` Bookworm logic. Kepler and other architectures now invoke specific installation functions directly without defaulting to unsupported driver versions (e.g., 535).
- Corrected NVIDIA legacy package name in `nvidia.sh`. Updated `_install_nvidia_bookworm_kepler()` to use `nvidia-tesla-470-driver` instead of deprecated Bullseye naming conventions for Debian 12.
- Replaced specific kernel header references (`linux-headers-$(uname -r)`) with meta-package `linux-headers-amd64` in `firmware.sh`. Fixes DKMS installation failures for Broadcom/WiFi drivers across multiple Debian versions.

modules/gpu/_helpers.sh

@@ -23,7 +23,7 @@ declare -A NVIDIA_FAMILY_MAP=(
 )
 
 detect_nvidia_arch() {
-    local pci_id="$1"
+    local pci_id="${1^^}"
     local prefix="${pci_id:0:2}"
     echo "${NVIDIA_FAMILY_MAP[$prefix]:-unknown}"
 }