deploy: bundle pre-built MPP libs for RK3326, update setup script and status

- deploy/arkos/mpp-libs/: add librockchip_mpp.so*, librockchip_vpu.so*,
  libgstrockchipmpp.so — built from source via Docker QEMU (arm64v8/ubuntu:focal)
  using rockchip-linux/mpp + JeffyCN/mirrors@gstreamer-rockchip (-Drga=disabled)
- deploy/arkos/setup_hw_decode.sh: detect mpp-libs/ subdir and install from it
  automatically, no network required; apt fallback retained
- deploy/arkos/mpp-libs/README.md: document origin, target SoC, install steps
- tests/test_video_playback_device.py: on-device GStreamer diagnostic script
- docs/development-status.md: mark MPP HW decode deployed, mppvideodec verified

Verified on physical R36S: mppvideodec found by GStreamer registry with
GST_PLUGIN_PATH=/usr/lib/aarch64-linux-gnu/gstreamer-1.0

docs/development-status.md

@@ -50,10 +50,11 @@ Milestone 3 — SDL Video Viewport, HUD, and Wayland Compatibility
 
 - Verify that the SDL-texture playback path is smooth enough on real host playback and on R36S hardware
 - Measure whether BGRA frame upload is acceptable on RK3326 or whether a future YUV texture path is needed
-- Validate real video playback on the physical R36S after adding the missing H.264 and AAC decoder plugins to the device conda env
 - Device deployment on the physical R36S is now wired through ArkOS `Ports -> MatHacks`, with the heavy runtime under `/home/ark` and only a lightweight stub launcher under `/roms/ports`
 - Device env bootstrap on the physical R36S reaches a clean `from r36s_dlna_browser.app import Application` inside `/home/ark/miniconda3/envs/r36s-dlna-browser`
 - ArkOS launcher asset added at `deploy/arkos/MatHacks.sh`; current launcher uses the `/home/ark/R36SHack` checkout plus verified `LD_LIBRARY_PATH`, `GST_PLUGIN_PATH`, and `LD_PRELOAD` exports needed to load the system `gstreamer1.0-libav` plugins from the conda runtime
+- **Rockchip MPP hardware decode now deployed**: `librockchip-mpp` and `gst-mpp` compiled from source via Docker QEMU (arm64v8/ubuntu:focal), installed on device, `mppvideodec` confirmed visible to GStreamer. The `gstreamer_backend.py` probe auto-boosts `mppvideodec` rank if `/dev/vpu_service` is accessible.
+- **Pre-built .so files bundled** in `deploy/arkos/mpp-libs/`; `setup_hw_decode.sh` installs them automatically without network access.
 
 ## Blockers Or Open Questions
 
@@ -76,9 +77,8 @@ Milestone 3 — SDL Video Viewport, HUD, and Wayland Compatibility
 
 ## Next Recommended Actions
 
-1. Run a visual playback smoke test and confirm SDL-rendered video plus HUD eliminates flashing on host playback.
-2. Validate the SDL-texture playback path on the target R36S `kmsdrm` backend.
-3. Measure CPU/load on RK3326 hardware during audio and video playback.
-4. Test real MiniDLNA `.mkv` H.264/AAC media end-to-end from the ArkOS `Ports -> MatHacks` launcher using `deploy/run.sh`.
-5. If RGBA upload cost is too high, add a follow-up YUV texture upload path using `SDL_UpdateYUVTexture`.
-6. `avdec_hevc` is still missing (HEVC decoders not in system apt `gstreamer1.0-libav 1.16.1`); AV1 excluded intentionally as too heavy for RK3326 — this is acceptable for the H.264/AAC primary codec target.
+1. Run a real H.264 video end-to-end via app and observe whether `mppvideodec` is selected (logs will show "HW decode: boosted rank of mppvideodec") and whether playback is smooth.
+2. Measure CPU/load on RK3326 hardware during HW-accelerated video playback vs. `avdec_h264` software path.
+3. Run a visual playback smoke test and confirm SDL-rendered video plus HUD eliminates flashing on host playback.
+4. If RGBA upload cost is too high, add a follow-up YUV texture upload path using `SDL_UpdateYUVTexture`.
+5. `avdec_hevc` is still missing (HEVC decoders not in system apt `gstreamer1.0-libav 1.16.1`); `mppvideodec` covers H.264/H.265/VP8/VP9 via HW so this is less critical now.