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/is.md

@@ -0,0 +1,25 @@
+---
+description: Analyze GitHub issues (bugs or feature requests)
+argument-hint: "<issue>"
+---
+Analyze GitHub issue(s): $ARGUMENTS
+
+For each issue:
+
+1. Add the `inprogress` label to the issue via GitHub CLI and assign the issue to the local `gh` user before analysis starts. If either action fails, report that explicitly and continue.
+2. Read the issue in full, including all comments and linked issues/PRs.
+3. Do not trust analysis written in the issue. Independently verify behavior and derive your own analysis from the code and execution path.
+
+4. **For bugs**:
+   - Ignore any root cause analysis in the issue (likely wrong)
+   - Read all related code files in full (no truncation)
+   - Trace the code path and identify the actual root cause
+   - Propose a fix
+
+5. **For feature requests**:
+   - Do not trust implementation proposals in the issue without verification
+   - Read all related code files in full (no truncation)
+   - Propose the most concise implementation approach
+   - List affected files and changes needed
+
+Do NOT implement unless explicitly asked. Analyze and propose only.