Fix stale repository structure diagram in DEVELOP.md (#366)

The "Repository Structure" section still described the pre-v3.0
multi-skill layout (source/skills/audit/SKILL.md, polish/SKILL.md, ...).
Updated it to match the current single skill/ directory and top-level
layout (cli/, site/, extension/, functions/, plugin/, etc.).

docs/DEVELOP.md

@@ -171,15 +171,17 @@ The skill-behavior suite runs three providers (claude-haiku-4-5, gpt-5.4-mini, g
 
 ```
 impeccable/
-  source/                          # Edit these! Source of truth
-    skills/                        # Skill definitions
-      frontend-design/
-        SKILL.md
-        reference/*.md             # Domain-specific references
-      audit/SKILL.md
-      polish/SKILL.md
-      ...
-  dist/                            # Generated output (gitignored)
+  skill/                           # Edit these! Source of truth
+    SKILL.src.md                   # Frontmatter, shared design laws, command router
+    reference/                     # One <command>.md per command + domain references
+    scripts/                       # Skill runtime scripts (hooks, context.mjs, etc.)
+    agents/                        # Nested subagent definitions
+  cli/                             # Standalone `impeccable` CLI (npm package)
+  site/                            # impeccable.style (Astro)
+  extension/                       # Chrome extension
+  functions/                       # Cloudflare Pages Functions
+  plugin/                          # Committed Claude Code plugin build output
+  dist/                            # Generated provider output (gitignored)
   scripts/
     build.js                       # Main orchestrator
     lib/