Drop the repo's duplicate pr skill

[bazauto]

What

Deletes .claude/skills/pr/SKILL.md. The global ~/.claude/skills/pr is now the only pr
skill for these repos.

Why

The two files were ~80% identical text — 3,533 bytes here against 3,614 globally — and the
global one opened with "A repo with its own pr skill overrides this one — use that
instead."

That handoff does not work. Invoking /pr in this repo today loaded the global skill, so
the repo-specific content in this file never arrived: run npm test from the root and why,
run /docs-sync, use the /verify agent. The flow only went right because CLAUDE.md
already says the same things. So the duplication was not buying repo-specific guidance, it was
either costing a second read or silently losing it.

Nothing is lost

• The root-vs-workspace npm test trap is in CLAUDE.md §Commands, in more detail than
  it was here — including that a backend-only run succeeds while the frontend suite never
  executes, which is the part that matters.
• /docs-sync, /verify, and "merge commits are disabled" are now stated generically in
  the global skill ("if the repo has a /docs-sync skill", "prefer the repo's /verify
  agent", and the rebase rule).
• .git/pr-body.md as the body location is in the global skill.

The global skill also changed

Not in this repo, but this PR is the reason, so it is recorded here. Measured across nine days
of transcripts, the PR flow was costing ~11 turns at peak context. Three fixes:

• Write the body file with the Write tool — never a heredoc. A cat > … <<'EOF' with
  <tags> and backticks in the body was executed as commands rather than written this
  session: 20k characters of shell errors, a stray git reset --hard, an npm install and a
  full e2e re-run. The single most expensive event in the flow, and the old skill warned that
  heredocs misbehave without ever saying what to use instead.
• gh pr merge --squash --auto instead of watching CI. Verified safe here:
  allow_auto_merge: true, and main requires test-and-lint with strict: true, so GitHub
  will not merge a red or stale PR. Same guarantee, zero further turns. The skill records the
  precondition, because without required status checks --auto merges immediately.
• Prefer /verify over inline suites, and filter the summary when running inline. One
  test:e2e run dumped 20k characters of vite ECONNREFUSED noise into a context that then
  re-reads it on every later turn.

gh pr checks --json is also now called out as unsafe: the field set varies by gh version
and an unsupported field fails silently, which reads as "no checks reported" while CI is
passing. That happened today and hid a green run for 13 minutes.

Not done here

PicoDCC/.claude/skills/pr/SKILL.md is the same duplication, and its CLAUDE.md already
carries both the CMake presets and the "CI does not cross-build firmware" rule that its skill
adds. It is safe to delete the same way, but it is a different repo and a separate PR.

Tests

No code change — documentation and tooling only. npm run lint clean; the suites are
unaffected and were run in full on #181 immediately before this branch (1500 backend, 328
frontend, 71 e2e).