Add update flake and skill creator skills

.claude/skills/update-flake/SKILL.md

@@ -0,0 +1,46 @@
+---
+name: update-flake
+description: Update nix flake inputs to latest versions, fix build breakage from upstream changes, build all NixOS machines, and run garbage collection. Use when the user wants to update nixpkgs, update flake inputs, upgrade packages, or refresh the flake lockfile.
+---
+
+# Update Flake
+
+## Workflow
+
+### 1. Update All Inputs
+
+The flake tracks `nixos-unstable`. Update everything at once:
+
+```bash
+nix flake update
+```
+
+### 2. Check for Breakage and Fix
+
+Build errors typically fall into these categories:
+
+- **Patches failing to apply**: Check `patches/` directory. Rebase or remove patches if the upstream issue was fixed.
+- **Nextcloud version bump**: Check `common/server/nextcloud.nix` for the pinned version (e.g. `pkgs.nextcloud32`). If nixpkgs dropped the current version, upgrade by exactly ONE major version. Notify the user.
+- **Removed/renamed packages or options**: Search nixpkgs history for migration guidance and apply fixes.
+- **stateVersion changes**: If ANY change requires incrementing `system.stateVersion`, `home.stateVersion`, or data migration — STOP and ask the user. Do not proceed.
+
+### 3. Build All Machines
+
+See [references/machines.md](references/machines.md). Get machine list and build each:
+
+```bash
+nix eval .#nixosConfigurations --apply 'x: builtins.attrNames x' --json
+nix build .#nixosConfigurations.<hostname>.config.system.build.toplevel --no-link
+```
+
+Fix any build failures before continuing.
+
+### 4. Garbage Collection
+
+```bash
+nix store gc
+```
+
+### 5. Summary
+
+Report: inputs updated, fixes applied, nextcloud changes, and anything needing user attention.

.claude/skills/update-flake/references/machines.md

@@ -0,0 +1,19 @@
+# Machine Build Reference
+
+## Listing Machines
+
+Get the current list dynamically:
+```bash
+nix eval .#nixosConfigurations --apply 'x: builtins.attrNames x' --json
+```
+
+## Building a Machine
+
+```bash
+nix build .#nixosConfigurations.<hostname>.config.system.build.toplevel --no-link
+```
+
+## Important Constraints
+
+- **stateVersion**: If any update requires incrementing `system.stateVersion` or `home.stateVersion`, or any data migration, STOP and ask the user. Do not proceed on your own.
+- **nextcloud**: Pinned to a specific version (e.g. `pkgs.nextcloud32`). Only upgrade one major version at a time. Notify the user when upgrading.