fix: coalesce pinch updates and stop live zoom write-back

Surface Aug6 diag showed sDrop=0 but ~220 same-ms dual ZOOM frames and √2 cur ping-pong from reading currentZoom back into pinch state. Flush once per microtask and embed gitSha in diagnostic meta.

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitea/workflows/ci.yml

@@ -220,7 +220,13 @@ jobs:
           HTTPS_PROXY: http://192.168.31.189:7890
           http_proxy: http://192.168.31.189:7890
           https_proxy: http://192.168.31.189:7890
-        run: flutter build windows --release
+        shell: powershell
+        run: |
+          $sha = if ($env:GITHUB_SHA) { $env:GITHUB_SHA.Substring(0, [Math]::Min(12, $env:GITHUB_SHA.Length)) } else { "unknown" }
+          $built = Get-Date -Format "yyyy-MM-ddTHH:mm:ssK"
+          flutter build windows --release `
+            --dart-define="BADNOTE_GIT_SHA=$sha" `
+            --dart-define="BADNOTE_BUILD_TIME=$built"
 
       - name: Show build output
         shell: powershell