refactor(halcon): single-skill plugin layout → invoke as /halcon (not /halcon:halcon)

Move SKILL.md + references/ scripts/ evals/ from skills/halcon/ up to the
plugin root. Per Claude Code plugins-reference, a plugin with SKILL.md at its
root and no skills/ subdir is auto-loaded as a single-skill plugin (v2.1.142+),
so the invocation name = frontmatter name = halcon → clean /halcon.
Bump plugin.json 2.0.0 → 2.0.1 so existing installs receive the update.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plugins/halcon/scripts/extract_toc.py

@@ -0,0 +1,34 @@
+"""Rebuild the bundled PDF table-of-contents index (references/pdf/_toc.json).
+
+Self-contained: reads every PDF bundled under the skill's references/pdf/ and
+writes the multi-level TOC next to them. Run after adding/updating manuals.
+
+    /mnt/c/Users/NAURA/.local/bin/uv.exe run --no-project --with pymupdf \
+        python .claude/skills/halcon/scripts/extract_toc.py
+"""
+import fitz, os, glob, json
+
+# references/pdf/ relative to this script (scripts/ -> ../references/pdf)
+HERE = os.path.dirname(os.path.abspath(__file__))
+PDF_DIR = os.path.normpath(os.path.join(HERE, "..", "references", "pdf"))
+OUT = os.path.join(PDF_DIR, "_toc.json")
+
+out = {}
+for p in sorted(glob.glob(os.path.join(PDF_DIR, "*.pdf"))):
+    name = os.path.basename(p)
+    try:
+        doc = fitz.open(p)
+        out[name] = {"pages": doc.page_count, "toc": doc.get_toc()}  # [level,title,page]
+        doc.close()
+    except Exception as e:
+        out[name] = {"error": str(e)}
+
+with open(OUT, "w", encoding="utf-8") as f:
+    json.dump(out, f, ensure_ascii=False, indent=1)
+
+for name, v in out.items():
+    if "error" in v:
+        print(f"{name}: ERROR {v['error']}")
+    else:
+        print(f"{name}: {v['pages']} pages, {len(v['toc'])} toc entries")
+print("wrote", OUT)