build: add canonical PortMaster packaging

docs/PORTMASTER-PERFORMANCE.md

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+# PortMaster performance profile
+
+The PortMaster launcher keeps the normal game profile on unknown and stronger
+hardware. It enables the low-end profile only when the Linux device tree
+reports one of the identifiers used by the Allwinner H616/H700 XX handhelds:
+
+- `allwinner,h616`
+- `sun50iw9p1`
+- `allwinner,sun50i-h700`
+
+The low-end launch profile passes these options to Godot:
+
+- `--single-window`
+- `--disable-vsync`
+- `--max-fps 30`
+- `--audio-output-latency 40`
+
+It also passes `NETFISHING_LOW_END=1`. The game responds by rendering the 3D
+world at 75 percent linear resolution with nearest-neighbor scaling. This
+reduces 3D pixel work by about 44 percent while the separately rendered UI
+retains its canonical resolution.
+
+Do not use Godot's low processor mode for this profile. It reduces idle CPU
+usage by sleeping between updates and is not a game-performance optimization.
+
+When adding another device family, record its exact NUL-separated device-tree
+`compatible` value from the hardware before extending the launcher match. Do
+not infer detection from a retail product name alone.