feat(nix): add kernel and memory tuning for amd system

Tune sysctl parameters for better I/O and memory performance:
- Lower swappiness to reduce disk swapping with zram
- Reduce vfs_cache_pressure to keep filesystem caches longer
- Adjust dirty page writeback ratios for SSD performance
- Configure zram with zstd compression

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

systems/x86_64-linux/amd/default.nix

@@ -65,9 +65,22 @@ with lib.metacfg;
     "electron-27.3.11"
   ];
 
-  # increase freezing timeout
+  # Kernel tuning
   boot.kernel.sysctl = {
     "power.pm_freeze_timeout" = 30000;
+    # Reduce swap usage (you have zram)
+    "vm.swappiness" = 10;
+    # Prefer keeping directory/inode caches
+    "vm.vfs_cache_pressure" = 50;
+    # Faster dirty page writeback
+    "vm.dirty_ratio" = 10;
+    "vm.dirty_background_ratio" = 5;
+  };
+
+  # SSD TRIM support
+  services.fstrim = {
+    enable = true;
+    interval = "weekly";
   };
 
   programs.steam = {
@@ -96,7 +109,12 @@ with lib.metacfg;
     cider-2
   ];
 
-  zramSwap.enable = true;
+  # zram swap with zstd compression for better performance
+  zramSwap = {
+    enable = true;
+    algorithm = "zstd";
+    memoryPercent = 50;
+  };
 
   services.ratbagd.enable = true;