feat(dllm): backend packaging, gallery index, CI matrix

Registers the dllm backend across every surface: backend gallery index
(cpu amd64+arm64 with manifest merge, cuda13, l4t-cuda13 for GB10-class
hardware; no darwin per engine scope), top-level Makefile targets,
bump_deps pin tracking for DLLM_VERSION, and the curated known-backends
list for /backends/known (pref-only: auto-detecting on .gguf would
shadow llama-cpp). Note: image builds and the nightly bump leg stay red
until github.com/mudler/dllm.cpp is published (planned at merge time).

Assisted-by: Claude Code (Fable 5)
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

.github/workflows/bump_deps.yaml

@@ -38,6 +38,10 @@ jobs:
             variable: "PARAKEET_VERSION"
             branch: "master"
             file: "backend/go/parakeet-cpp/Makefile"
+          - repository: "mudler/dllm.cpp"
+            variable: "DLLM_VERSION"
+            branch: "main"
+            file: "backend/go/dllm/Makefile"
           - repository: "leejet/stable-diffusion.cpp"
             variable: "STABLEDIFFUSION_GGML_VERSION"
             branch: "master"