fix(bump-version): update default.nix version (#502)

- Add missing support for scripted default.nix version update to
  bump-version.sh

scripts/bump-version.sh

@@ -230,7 +230,13 @@ main() {
             "# bd-hooks-version: $NEW_VERSION"
     done
 
-    # 10. Update CHANGELOG.md
+    # 10. Update default.nix
+    echo "  • default.nix"
+    update_file "default.nix" \
+        "version = \"$CURRENT_VERSION\"" \
+        "version = \"$NEW_VERSION\""
+
+    # 11. Update CHANGELOG.md
     echo "  • CHANGELOG.md"
     update_changelog "$NEW_VERSION"
 
@@ -253,6 +259,7 @@ main() {
         "$(grep '__version__ = ' integrations/beads-mcp/src/beads_mcp/__init__.py | sed 's/.*"\(.*\)".*/\1/')"
         "$(jq -r '.version' npm-package/package.json)"
         "$(grep '# bd-hooks-version: ' cmd/bd/templates/hooks/pre-commit | sed 's/.*: \(.*\)/\1/')"
+        "$(grep 'version = ' default.nix | sed 's/.*"\(.*\)".*/\1/')"
     )
 
     ALL_MATCH=true
@@ -372,7 +379,8 @@ main() {
                 integrations/beads-mcp/src/beads_mcp/__init__.py \
                 npm-package/package.json \
                 README.md \
-                cmd/bd/templates/hooks/*
+                cmd/bd/templates/hooks/* \
+                default.nix
 
         # Add PLUGIN.md if it exists
         if [ -f "PLUGIN.md" ]; then
@@ -391,6 +399,7 @@ Updated all component versions:
 - Plugin: $CURRENT_VERSION → $NEW_VERSION
 - MCP server: $CURRENT_VERSION → $NEW_VERSION
 - npm package: $CURRENT_VERSION → $NEW_VERSION
+- Nix package: $CURRENT_VERSION → $NEW_VERSION
 - Documentation: $CURRENT_VERSION → $NEW_VERSION
 
 Generated by scripts/bump-version.sh"