chore: ignore throwaway build worktrees

observer-firmware had a .build-wt-<sha> worktree committed as a gitlink, which
made every CI checkout warn "No url found for submodule path ... in .gitmodules"
and broke `git submodule` in fresh clones. This branch has no such entry; ignore
the pattern so it stays that way, and skip it in both channels' paths-ignore
since a build worktree can never change the binaries.

The production build workflow is taken from observer-firmware verbatim, keeping
the copy on this branch identical and conflict-free on promotion.

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

@@ -38,6 +38,9 @@ on:
       - 'LICENSE'
       - '.vscode/**'
       - '.claude/**'
+      # Throwaway build worktrees never affect the binaries.
+      - '.build-wt-*'
+      - '.build-wt-*/**'
 
 # Own group: serialize beta builds against each other only. Concurrency groups are
 # repo-wide, not per-branch, so sharing one with the production workflows let an

.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