[pull] main from getsentry:main - #426

* docs(agents): Fold pr.mdc into the create-java-pr skill

The pr.mdc rule file and the create-java-pr skill described the same
six-step PR workflow, and both inlined a copy of the PR template and the
changelog subsection table. Nobody on the team uses Cursor, so the
rule/skill split earned nothing and the two copies had already drifted:
both inlined templates were missing the "Public API changes reviewed by
another Mobile SDK team member" checklist item that
.github/pull_request_template.md has gained since.

Delete pr.mdc and give its content one home each. The conventions the
skill was missing (allowed commit types, PR title format, changelog
rebase caveat) move into the skill. The stacked-PR workflow moves to a
references file the skill loads on demand, so the common standalone-PR
path no longer carries 150 lines that only apply to stacks.

The skill now reads .github/pull_request_template.md instead of
reproducing it, leaving one copy that cannot drift.

#skip-changelog

* docs(agents): Trim generic stacking guidance from stacked-prs.md

The reference file mixed two kinds of content: the standard Graphite-style
stacking workflow, which any agent can reconstruct from general knowledge and
`gh` usage, and the parts specific to this repo. The generic half diluted the
half that matters.

Drop the chain-walking recipe, the branch naming convention, the generic
create/merge/sync steps, and the restatement of the stack shape. Keep what is
not derivable: why the collection branch exists (`main` is squash-only, which
conflicts repeatedly when syncing a stack), the title and stack list formats,
and the permission-pattern constraint on editing PR bodies.

Collect the four destructive-operation warnings under one heading instead of
leaving them scattered across three sections, and point SKILL.md at the
surviving section names.

#skip-changelog

* docs(agents): Fix defects found by dry-running the PR skill

Ran fresh agents through "create a PR" and "create a stacked PR" against
the deduped docs, stopping each before the first mutating action. Both
paths loaded the intended files, but four defects surfaced:

- SKILL.md named stacked-prs.md the source of truth for branch naming,
  which that file never covered. Corrected to title naming; the branch
  rule stays in Step 1, where the branch is created.
- Four passages referenced the collection branch PR, but no step ever
  opened it. Added next to the branch creation, with its title and
  merge-reminder exceptions.
- The PR-description editing rule was stated three times and had already
  drifted. It now lives once in SKILL.md, which both the standalone and
  stacked paths read, and stacked-prs.md points back to it.
- AGENTS.md rule 7 told agents to propose but not execute a commit while
  the create-java-pr skill commits, pushes, and opens the PR, leaving two
  terminal states for one request. Scoped rule 7 to implementation work.

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

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