Add build version indicator to sidebar menu

Display commit date and short hash (e.g., "2026-01-08 fb59ef7") below
the ANIMALTRACK title in the sidebar. In development, reads from git
directly; in Docker, reads from BUILD_DATE/BUILD_COMMIT env vars
injected at build time from the Nix flake.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docker.nix

@@ -1,4 +1,4 @@
-{ pkgs, pythonEnv, python }:
+{ pkgs, pythonEnv, python, buildDate ? "unknown", buildCommit ? "unknown" }:
 
 let
   # Build animaltrack as a package
@@ -59,6 +59,8 @@ pkgs.dockerTools.buildImage {
       "PATH=${pkgs.lib.makeBinPath [ pkgs.busybox pkgs.bash pkgs.sqlite pythonEnv animaltrack ]}"
       "PYTHONPATH=${pythonEnv}/${pythonEnv.sitePackages}:${animaltrack}/${pythonEnv.sitePackages}"
       "PYTHONUNBUFFERED=1"
+      "BUILD_DATE=${buildDate}"
+      "BUILD_COMMIT=${buildCommit}"
     ];
     ExposedPorts = {
       "5000/tcp" = {};

flake.nix

@@ -67,7 +67,12 @@
     in
     {
       packages.${system} = {
-        dockerImage = import ./docker.nix { inherit pkgs pythonEnv python; };
+        dockerImage = let
+          buildDate = let
+            d = self.lastModifiedDate or "00000000000000";
+          in "${builtins.substring 0 4 d}-${builtins.substring 4 2 d}-${builtins.substring 6 2 d}";
+          buildCommit = self.shortRev or self.dirtyShortRev or "unknown";
+        in import ./docker.nix { inherit pkgs pythonEnv python buildDate buildCommit; };
       };
 
       devShells.${system}.default = pkgs.mkShell {

src/animaltrack/build_info.py

@@ -0,0 +1,34 @@
+# ABOUTME: Provides build information (date + commit hash) for version display.
+# ABOUTME: Reads from env vars (Docker) or git (development).
+
+import os
+import subprocess
+
+
+def get_build_info() -> str:
+    """Returns build info in '2025-01-08 fb59ef7' format.
+
+    Checks BUILD_DATE and BUILD_COMMIT env vars first (set by Docker),
+    then falls back to reading git info at runtime (development).
+    Returns 'unknown' if neither source is available.
+    """
+    build_date = os.environ.get("BUILD_DATE")
+    build_commit = os.environ.get("BUILD_COMMIT")
+
+    if build_date and build_commit:
+        return f"{build_date} {build_commit}"
+
+    # Try git at runtime (development mode)
+    try:
+        result = subprocess.run(
+            ["git", "log", "-1", "--format=%cs %h"],
+            capture_output=True,
+            text=True,
+            timeout=5,
+        )
+        if result.returncode == 0 and result.stdout.strip():
+            return result.stdout.strip()
+    except (subprocess.SubprocessError, FileNotFoundError, OSError):
+        pass
+
+    return "unknown"

src/animaltrack/web/templates/sidebar.py

@@ -4,6 +4,7 @@
 from fasthtml.common import A, Button, Div, Nav, Script, Span, Style
 from fasthtml.svg import Path, Svg
 
+from animaltrack.build_info import get_build_info
 from animaltrack.models.reference import UserRole
 from animaltrack.web.templates.icons import EggIcon, FeedIcon, MoveIcon
 
@@ -213,7 +214,8 @@ def Sidebar(  # noqa: N802
     return Nav(
         # Logo/Brand
         Div(
-            Span("ANIMALTRACK", cls="text-amber-600 font-bold tracking-wider text-sm"),
+            Div("ANIMALTRACK", cls="text-amber-600 font-bold tracking-wider text-sm"),
+            Div(get_build_info(), cls="text-stone-600 text-[10px] tracking-wide"),
             cls="px-4 py-4 border-b border-stone-800",
         ),
         # Primary navigation