Pin the formatter, and stop it editing the record

The first CI run went red on `ruff format --check`, on a tree that was clean on
this machine. Three separate problems, all found by pushing.

`ruff>=0.4` is not a pin. CI installed 0.16.6 where the laptop had 0.15.18, and
0.16 formats Python code blocks inside Markdown while 0.15 leaves them alone — so
the two disagreed about whether the repository was formatted, which is the one
thing a formatter exists to settle. Pinned to the 0.16 line. Dependabot will
offer the next one, and CI will say whether it is safe.

The file it tripped over is `docs/survey-ui-consistency.md`, which quotes four
lines of a dialog call as it looked on 22 August. That excerpt is a fragment —
two arguments, no call around them — so the formatter parsed it as two statements
and rewrote them into a tuple and an assignment that never existed anywhere. The
surveys are dated records of a past state, so `docs/` is now excluded: a
formatter editing a quotation is not tidying, it is falsifying.

And the installer workflow was firing for branches it had no business building.
Dependabot opened three action bumps within a minute of the push; each one edits
`.github/workflows/installers.yml`, each matched its own path filter, and each
started a five-platform build. `branches: [main]` stops it.

Everything else was green on the first try, including the part that was actually
uncertain: all seven test legs passed, macOS among them, and the installers built
on Windows, macOS on Apple silicon, and Linux on both x64 and arm64 — so the
uConsole build works and the ARM runner was available after all.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/installers.yml

@@ -14,6 +14,10 @@ on:
   # Only when the packaging itself changes. Three operating systems is not something to
   # spend on every commit while the repository is private and minutes are metered.
   push:
+    # `main` only. Without this, every Dependabot branch that touches this file — which
+    # is every action bump — starts a five-platform build, and three of those legs are
+    # billed at 2x and 10x.
+    branches: [main]
     paths:
       - "packaging/**"
       - ".github/workflows/installers.yml"