fix(docs): correct mermaid diagram to show polecats as worktrees not clones

The rig-level mermaid diagram incorrectly labeled polecats as git clone
when they are actually git worktrees from Mayor's clone. This now matches
the ASCII diagram which correctly describes them as worktrees.

🤖 Generated with Claude Code

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/architecture.md

@@ -288,8 +288,8 @@ graph TB
         Beads[".beads/"]
 
         subgraph Polecats["polecats/"]
-            Nux["Nux/<br/>(git clone)"]
-            Toast["Toast/<br/>(git clone)"]
+            Nux["Nux/<br/>(worktree)"]
+            Toast["Toast/<br/>(worktree)"]
         end
 
         subgraph Refinery["refinery/"]