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>

.github/scripts/paged-canary-apply.sh

@@ -1,14 +1,14 @@
 #!/usr/bin/env bash
 #
 # paged-canary-apply.sh - apply the vendored paged-attention patch series
-# (backend/cpp/llama-cpp/patches/paged/0001-0030) to a llama.cpp checkout, the
+# (backend/cpp/llama-cpp-localai-paged/patches/paged/0001-0030) to a llama.cpp checkout, the
 # same way the build does, but tolerating the ONE known-benign pre-existing
 # quirk in the series. Used by the early-warning canary
 # (.github/workflows/llama-cpp-paged-canary.yml) so it only goes red on a REAL
 # upstream break, never on that quirk.
 #
 # Usage: paged-canary-apply.sh <llama.cpp-checkout-dir> <patches-dir>
-#   <patches-dir> is normally backend/cpp/llama-cpp/patches (it holds the
+#   <patches-dir> is normally backend/cpp/llama-cpp-localai-paged/patches (it holds the
 #   top-level base series 0*.patch, currently empty, and the paged/ subseries).
 #
 # Exit 0  = the whole series applied -> patches still fit upstream.
@@ -27,7 +27,7 @@
 # missing-file hunk rejects the whole patch - and because 0021/0022/0026/0028
 # build on 0019's code, the rejection cascades to them too. This is a
 # PRE-EXISTING shipped-series defect, present identically on every pin, NOT an
-# upstream break (see backend/cpp/llama-cpp/patches/paged/PIN_SYNC_c299a92c.md
+# upstream break (see backend/cpp/llama-cpp-localai-paged/patches/paged/PIN_SYNC_c299a92c.md
 # and README.md). We exclude ONLY that dev-doc path and still
 # apply 0019's real code hunks atomically, so a genuine code-hunk break in 0019
 # still fails the canary. prepare.sh tolerates the same hunk via
@@ -53,7 +53,7 @@ apply_one() {
   echo "paged-canary: applying $(basename "$p")"
   if ! git apply --verbose "$@" "$p"; then
     echo "::error::paged patch no longer applies to the upstream llama.cpp tip: $(basename "$p")"
-    echo "::error::upstream drifted past the vendored paged series - run a PIN_SYNC (backend/cpp/llama-cpp/patches/paged/PIN_SYNC_c299a92c.md), do NOT bump the pin blindly"
+    echo "::error::upstream drifted past the vendored paged series - run a PIN_SYNC (backend/cpp/llama-cpp-localai-paged/patches/paged/PIN_SYNC_c299a92c.md), do NOT bump the pin blindly"
     exit 1
   fi
 }