chore: track .env.example (Task Master template, no secrets)

The .gitignore had three competing rules — .env.* (line 70), *.env.*
(line 259), and a stale negation !.env.example (line 71) that lost to
the later rules. Adding the negation at the end of the file so it wins.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -324,3 +324,7 @@ dev-debug.log
 .taskmaster/state.json
 .taskmaster/reports/
 
+# Always track .env.example (template, no secrets) — must come AFTER the
+# .env.* / *.env.* rules above which would otherwise re-ignore it.
+!.env.example
+