Rename ralph-wiggum plugin to ralph-loop per legal guidance (#142)

- Rename plugin from "ralph-wiggum" to "ralph-loop" to avoid trademark concerns
- Update all internal references to use "Ralph Loop" as the prominent name
- Keep explanatory text noting it "implements the Ralph Wiggum technique" (allowed)
- Rename plugin directory from plugins/ralph-wiggum to plugins/ralph-loop
- Update marketplace.json with new plugin name and source path
- Update plugin-dev documentation references

This change follows legal's recommendation to replace "Wiggum" with "Loop"
in the plugin name while still explaining the technique origin.

Slack thread: https://anthropic.slack.com/archives/C09KU300P7F/p1767741142753959

Co-authored-by: Claude <noreply@anthropic.com>

plugins/ralph-loop/commands/cancel-ralph.md

@@ -0,0 +1,18 @@
+---
+description: "Cancel active Ralph Loop"
+allowed-tools: ["Bash(test -f .claude/ralph-loop.local.md:*)", "Bash(rm .claude/ralph-loop.local.md)", "Read(.claude/ralph-loop.local.md)"]
+hide-from-slash-command-tool: "true"
+---
+
+# Cancel Ralph
+
+To cancel the Ralph loop:
+
+1. Check if `.claude/ralph-loop.local.md` exists using Bash: `test -f .claude/ralph-loop.local.md && echo "EXISTS" || echo "NOT_FOUND"`
+
+2. **If NOT_FOUND**: Say "No active Ralph loop found."
+
+3. **If EXISTS**:
+   - Read `.claude/ralph-loop.local.md` to get the current iteration number from the `iteration:` field
+   - Remove the file using Bash: `rm .claude/ralph-loop.local.md`
+   - Report: "Cancelled Ralph loop (was at iteration N)" where N is the iteration value