Add a PR stack skill

[r0adkll]

Adds a pr-stack agent skill for opening and maintaining pull requests, especially stacks of dependent PRs, and a script that gives every PR in a stack a Stack section.

What changed

• .claude/skills/pr-stack/SKILL.md collects what worked while building the Break-up the CampfireSettings monolith into appScope/userScope layers #607 stack:
  • Before pushing: ask first; check each branch on its own (ktlint, app compiles, jvmTest test); run the device tester against the testbed for behavior changes, including the upgrade path for storage changes.
  • Changelog: one entry per feature across the stack; fixes found along the way get their own entry in the PR that fixes them.
  • Commit signing: when 1Password fails, wait for the user to retry. Never skip signing, and no co-author trailers.
  • Descriptions: a lead paragraph, then What changed / Verification / Follow-ups. Closes #N goes only in the top PR, because GitHub closes issues only on merge into main.
  • Opening a stack bottom-up, then editing PRs through gh api, because gh pr edit fails here.
  • Restacking with rebase --onto from each branch's old tip. main is squash-only and deletes branches on merge, so after a parent merges, GitHub retargets its children to main but their branches still carry the parent's original commits.
  • Closing or drafting superseded PRs.
• scripts/stack_section.py writes the Stack section.

  • It builds the stack tree from the open PRs' base and head branches, starting from any PR in it.

  • It renders the same nested list on every PR, indented by position, with [This PR] marking the one being viewed:

    ## Stack
    
    - #1189
      - #1195
        - [This PR] #1196
          - #1197
            - #1198
            - #1199

  • The section sits at the top of the description between hidden <!-- pr-stack:start --> / <!-- pr-stack:end --> markers, so reruns replace it in place.

  • Merged and closed PRs drop out of the list, and the section is removed once a PR is alone.

  • It prints what it would change unless given --apply.

There's no app change, so no changelog entry.

Verification

• A dry run against the open Break-up the CampfireSettings monolith into appScope/userScope layers #607 stack (Split CampfireSettings into focused settings interfaces #1189, Organize settings into packages and write through setters #1195–Keep theme, library view and per-book settings per account #1200) produced the right tree for all seven PRs, including the fork where Apply skip-time changes to a running player #1198 and Store settings in DataStore #1199 both build on Make the settings API flow-only #1197.
• Offline checks of the body editing cover:
  • inserting the section at the top;
  • replacing it in place, including GitHub's \r\n line endings;
  • a rerun changing nothing;
  • the [This PR] marker moving between PRs;
  • removing the section when a PR is alone in its stack.

🤖 Generated with Claude Code

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Code Coverage

Total Project Coverage	23.49%	❌

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Android APK @ 771a27e