refactor(paged): stock llama-cpp is patch-free; paged backend owns its patch series

Move ALL paged-attention content out of the stock backend/cpp/llama-cpp
backend and into backend/cpp/llama-cpp-localai-paged, so the stock backend is
pure upstream llama.cpp and the paged backend owns and applies its own vendored
patch series.

- Delete the dead early-exploration scaffold backend/cpp/llama-cpp/paged/
  (kernel/w4a16 Marlin scaffold, standalone paged_kv_manager, bench/loadgen,
  its own 0001-0002 patches, dense-era design docs, tests). Zero references
  repo-wide.
- Move backend/cpp/llama-cpp/patches/ (the 28-patch paged series + paged/README
  + 3 operational docs, plus the kernel/ scaffold patch and the top-level paged
  README/BENCHMARKS) to backend/cpp/llama-cpp-localai-paged/patches/. The stock
  backend keeps no patches/ dir; it had no non-paged base patches.
- Purify the stock backend: remove the LLAMA_PAGED make variable, the
  patches/paged apply loop, and the LLAMA_PAGED passthrough to prepare.sh;
  remove the paged-series handling from prepare.sh. The stock llama.cpp target
  now only clones the pin and applies its own (currently empty) base patches/
  series. The runtime paged option hooks in the shared grpc-server.cpp are
  untouched (inert without the patches).
- The paged backend's Makefile now applies its OWN patches/paged/0*.patch onto
  each freshly cloned tree via strict git apply (apply-paged-patches), after the
  copied stock infra clones the pin and applies base patches.
- Repoint every reference to the old patches/paged path: the upstream canary
  workflow + apply script, bump_deps.yaml, gallery/index.yaml, the docs,
  backend/index.yaml, backend-matrix.yml, the top-level Makefile comments, and
  the moved PIN_SYNC / README docs. Drop the now-removed LLAMA_PAGED=on
  build-toggle from comments.

Verified: the full 28-patch series applies strict-clean (git apply, exit 0) to
a clean ggml-org/llama.cpp checkout at the pinned c299a92c, and the repointed
canary apply script resolves and applies the series end to end.

Assisted-by: Claude:opus-4.8 [Claude Code]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

backend/cpp/llama-cpp/prepare.sh

@@ -2,30 +2,18 @@
 
 ## Patches
 
-## Apply patches: the base `patches/` series, then the gated `patches/paged/`
-## series (default on; LLAMA_PAGED=off skips it). Only *.patch files are applied
-## (docs/dirs like patches/paged/ and *.md are skipped). The Makefile `llama.cpp`
-## target already `git apply`s these at checkout, so each apply is guarded by a
-## sentinel and skipped when already present - re-applying git-format patches with
-## `patch` fuzzily duplicates hunks (redefinition errors). This block only does
-## real work if prepare.sh is run against an unpatched checkout.
+## Apply the base `patches/` series (top-level *.patch only; *.md/dirs skipped).
+## The stock llama-cpp backend is patch-free by default, so this normally does
+## nothing. The Makefile `llama.cpp` target already `git apply`s any base patch
+## at checkout, so each apply here is `-N` (skip already-applied): re-applying a
+## git-format patch with `patch` would fuzzily duplicate hunks. This block only
+## does real work if prepare.sh is run against an unpatched checkout.
 if [ -d "patches" ]; then
     for patch in patches/*.patch; do
         [ -e "$patch" ] || continue
         echo "Applying patch $patch"
         patch -d llama.cpp/ -p1 -N -r - < "$patch" || true
     done
-    if [ "${LLAMA_PAGED:-on}" != "off" ] && [ -d "patches/paged" ]; then
-        if [ -f llama.cpp/src/paged-kv-manager.cpp ]; then
-            echo "paged-attention patch series already applied (sentinel present) - skipping re-apply"
-        else
-            for patch in patches/paged/*.patch; do
-                [ -e "$patch" ] || continue
-                echo "Applying paged patch $patch"
-                patch -d llama.cpp/ -p1 -N -r - < "$patch" || true
-            done
-        fi
-    fi
 fi
 
 set -e