feat(sproutclaw): modularize webui, extensions, and agent config layout

Restructure local extensions into per-feature directories, split WebUI
into backend modules with slash commands and systemd support, and track
prompts/skills under .pi/agent for portable Gitea deployment.

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

.pi/agent/prompts/pr.md

@@ -0,0 +1,37 @@
+---
+description: Review PRs from URLs with structured issue and code analysis
+argument-hint: "<PR-URL>"
+---
+You are given one or more GitHub PR URLs: $@
+
+For each PR URL, do the following in order:
+1. Add the `inprogress` label to the PR via GitHub CLI before analysis starts. If adding the label fails, report that explicitly and continue.
+2. Read the PR page in full. Include description, all comments, all commits, and all changed files.
+3. Identify any linked issues referenced in the PR body, comments, commit messages, or cross links. Read each issue in full, including all comments.
+4. Analyze the PR diff. Read all relevant code files in full with no truncation and compare against the diff. Do not fetch PR file blobs unless a file is missing on main or the diff context is insufficient. Include related code paths that are not in the diff but are required to validate behavior.
+5. Do not check for a changelog entry. Per CONTRIBUTING.md, contributor PRs must not edit `CHANGELOG.md` — the maintainer adds the entry when merging.
+6. Check if packages/coding-agent/README.md, packages/coding-agent/docs/*.md, packages/coding-agent/examples/**/*.md require modification. This is usually the case when existing features have been changed, or new features have been added.
+7. Provide a structured review with these sections:
+   - What it does: one short paragraph describing the change and its intent.
+   - Good: solid choices or improvements.
+   - Bad: concrete issues, regressions, missing tests, or risks.
+   - Ugly: subtle or high impact problems.
+   - Tests: what is covered, what is missing, and whether existing tests are adequate.
+   - Open questions for you: only things blocking a merge decision that need the user's input. Omit the section entirely if there are none.
+
+Output format per PR:
+PR: <url>
+What it does:
+- ...
+Good:
+- ...
+Bad:
+- ...
+Ugly:
+- ...
+Tests:
+- ...
+Open questions for you:
+- ...
+
+If no issues are found, say so under Bad and Ugly.