chore: Nix, mise, CI configuration (#129)

* chore: update Nix flake and setup mise for toolchains

* ci: use workflows

.github/workflows/build.yml

@@ -1,7 +1,8 @@
 on:
   push:
     branches:
-      - "**"
+      - main
+  pull_request:
 
 jobs:
   build:
@@ -15,16 +16,10 @@ jobs:
       - name: Checkout assets
         run: git -c submodule."assets".update=checkout submodule update --init assets
 
-      - name: Install pnpm
-        uses: pnpm/action-setup@v4
+      - name: Setup Mise
+        uses: immich-app/devtools/actions/use-mise@cd24790a7f5f6439ac32cc94f5523cb2de8bfa8c # use-mise-action-v1.1.0
         with:
-          run_install: false
-
-      - name: Install Node.js
-        uses: actions/setup-node@v4
-        with:
-          node-version: 22
-          cache: "pnpm"
+          github-token: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Install dependencies
         run: pnpm install

.github/workflows/git-town.yml

@@ -0,0 +1,19 @@
+name: Git Town
+
+on:
+  pull_request:
+
+jobs:
+  git-town:
+    name: Display the branch stack
+    runs-on: ubuntu-slim
+
+    if: ${{ !startsWith(github.head_ref, 'release-please--') }}
+
+    permissions:
+      contents: read
+      pull-requests: write
+
+    steps:
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+      - uses: stoatchat/action-git-town@4bc5c942e4603bffa0806b51d5fe5f0bc5deb0ac