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/__init__.py

@@ -0,0 +1,13 @@
+"""The pieces behind ctf_status.py, in the order the data flows through them:
+
+  config.py     read .env and the environment
+  gitlab.py     list the group's repos, download README.md and description.yml
+  challenge.py  turn a README header into a Challenge (status, category, ...)
+  checks.py     decide what is wrong with a challenge, and whether to believe
+                a Testing Ready+ status  <- the rules live here
+  overview.py   run all of the above over every repo, group and sort the result
+  terminal.py   the terminal summary
+  markdown.py   the HedgeDoc note
+  challs.py     challs.txt for the deployment repo
+  hedgedoc.py   write the note into HedgeDoc
+"""