Split ctf_status.py into a tracker package, config from .env only

ctf_status.py is now just the command line; the work lives in tracker/.
The rules that decide whether a challenge is believed are in
tracker/checks.py, one function per rule, listed in README_CHECKS and
REPO_CHECKS. Output is unchanged.

Read the config from .env only (ctf_status.env.example -> .env.example),
let single_run_lock() hold its own lock files, and rewrite the README as
a short overview of what the repo does and how to run it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tracker/config.py

@@ -0,0 +1,35 @@
+"""Config from .env next to ctf_status.py; environment variables override it."""
+from __future__ import annotations
+
+import os
+import sys
+from pathlib import Path
+
+CFG_KEYS = ("GITLAB_GROUP_URL", "GITLAB_TOKEN")
+OPT_KEYS = ("HEDGEDOC_NOTE", "HEDGEDOC_TAGS", "TITLE",
+            "CHALLS_REPO_URL", "CHALLS_PATH", "CHALLS_BRANCH")
+# the names a plain `.env` tends to use for the same thing
+ALIASES = {"GL_PAT": "GITLAB_TOKEN", "GITLAB_URL": "GITLAB_GROUP_URL"}
+DEFAULT_TAGS = "Logistics, h4tum CTF 2026"
+DEFAULT_TITLE = "CTF challenge tracking"
+DEFAULT_CHALLS_PATH = "2026/challs.txt"
+
+
+def load_env() -> dict:
+    cfg = {}
+    env_file = Path(__file__).parent.parent / ".env"  # the repo, next to ctf_status.py
+    if env_file.exists():
+        for line in env_file.read_text().splitlines():
+            line = line.strip()
+            if not line or line.startswith("#") or "=" not in line:
+                continue
+            k, v = line.split("=", 1)
+            k = k.strip().upper()
+            cfg.setdefault(ALIASES.get(k, k), v.strip().strip("'\""))
+    for k in CFG_KEYS + OPT_KEYS + tuple(ALIASES):
+        if os.environ.get(k):
+            cfg[ALIASES.get(k, k)] = os.environ[k]
+    missing = [k for k in CFG_KEYS if not cfg.get(k)]
+    if missing:
+        sys.exit(f"missing config: {', '.join(missing)} (see .env.example)")
+    return cfg