chore: untrack the .build-wt-028a5dca build worktree

It was committed as a gitlink (mode 160000) with no .gitmodules entry, so every
CI checkout's cleanup step ended with "No url found for submodule path
'.build-wt-028a5dca'" and a git exit-128 warning, and `git submodule` commands
failed in fresh clones. The worktree itself is removed locally; commit 028a5dca
stays reachable from this branch, so no history is affected.

Ignore the pattern so a throwaway build worktree cannot be committed again, and
add it to paths-ignore since such a directory can never change the binaries —
that also keeps this removal from triggering a pointless full rebuild.

.github/workflows/build-observer-firmwares.yml

@@ -25,6 +25,9 @@ on:
       - 'LICENSE'
       - '.vscode/**'
       - '.claude/**'
+      # Throwaway build worktrees never affect the binaries.
+      - '.build-wt-*'
+      - '.build-wt-*/**'
 
 # Own group: serialize builds against each other only. Do NOT share this group
 # with sync-flasher-content.yml — a mixed code+docs commit triggers both, and a

.gitignore

@@ -24,3 +24,6 @@ platformio.local.ini
 .claude/*
 .cursorrules
 src/helpers/esp32/WebConfigHtml.h
+# Throwaway build worktrees; committing one adds a stray gitlink that makes every
+# CI checkout warn "No url found for submodule path ... in .gitmodules".
+.build-wt-*/