Add T490 hardware configuration and docs

- modules/t490.nix: TLP power management, CPU throttling (throttled), S3 sleep,
  remote Nix builders (cluster), fwupd, fprintd, fprintd, Syncthing, Tailscale,
  Intel VA-API, TrackPoint sensitivity, PipeWire defaults
- flake.nix: add nixos-hardware input, import T490 module + nixos-hardware
- docs/T490-HARDWARE.md: WiFi variants, graphics, audio, fingerprint, sleep guide
- docs/T490-BATTERY.md: TLP config, threshold strategy, real-world battery numbers
- docs/T490-OFFLOADING.md: local vs cluster split, remote builder setup
- MIGRATION.md: add T490 post-install steps (fwupd, fprint, remote build key)
- README.md: reflect new module and docs structure

MIGRATION.md

@@ -88,6 +88,27 @@ curl -s http://localhost:3987/health  # should return ok
 # Discord: @mention Marcus in #speaker-site
 ```
 
+### 8. T490 hardware setup
+```bash
+# Firmware updates (BIOS, EC, Thunderbolt, fingerprint reader)
+fwupdmgr refresh && fwupdmgr update
+# May need to disable Boot Order Lock in BIOS first
+
+# Enroll fingerprint
+fprintd-enroll
+
+# Check sleep mode
+cat /sys/power/mem_sleep
+# Should show [deep] if S3 is available and configured
+
+# Set up remote build SSH key
+sudo ssh-keygen -t ed25519 -f /root/.ssh/remote-build -N ""
+# Copy /root/.ssh/remote-build.pub to each cluster node's /root/.ssh/authorized_keys
+
+# Set up Syncthing (pair with cluster nodes for vault sync)
+systemctl --user enable --now syncthing
+```
+
 ## Files to NOT transfer
 These contain caches, build artifacts, or macOS-specific junk:
 - `~/Library/` — macOS only
@@ -113,3 +134,8 @@ These contain caches, build artifacts, or macOS-specific junk:
 - [ ] Hyprland: SUPER+D opens rofi, SUPER+Return opens ghostty+zellij
 - [ ] Discord: @mention Marcus → gets a reply
 - [ ] Wallpaper appears after login
+- [ ] Firmware updated (`fwupdmgr update`)
+- [ ] Fingerprint enrolled (`fprintd-enroll`)
+- [ ] S3 sleep working (`cat /sys/power/mem_sleep` shows `[deep]`)
+- [ ] Remote Nix builders working (`nix build --rebuild nixpkgs#hello`)
+- [ ] Syncthing running for vault sync