feat: add self-update command and bump to 2.0.1

- Add `coinhunter update` CLI command for pipx/pip upgrade
- README: document update behavior and recommend pipx install
- Dynamic version badge with cacheSeconds=60
- Version bump: 2.0.0 → 2.0.1

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/coinhunter/runtime.py

@@ -4,6 +4,9 @@ from __future__ import annotations
 
 import json
 import os
+import shutil
+import subprocess
+import sys
 from dataclasses import asdict, dataclass, is_dataclass
 from datetime import date, datetime
 from pathlib import Path
@@ -50,3 +53,17 @@ def json_default(value: Any) -> Any:
 
 def print_json(payload: Any) -> None:
     print(json.dumps(payload, ensure_ascii=False, indent=2, sort_keys=True, default=json_default))
+
+
+def self_update() -> dict[str, Any]:
+    if shutil.which("pipx"):
+        cmd = ["pipx", "upgrade", "coinhunter"]
+    else:
+        cmd = [sys.executable, "-m", "pip", "install", "--upgrade", "coinhunter"]
+    result = subprocess.run(cmd, capture_output=True, text=True)
+    return {
+        "command": " ".join(cmd),
+        "returncode": result.returncode,
+        "stdout": result.stdout.strip(),
+        "stderr": result.stderr.strip(),
+    }