fix(docker): honour docker-compose.override.yml in Start-Codeman.sh

Naming a Compose file with -f disables Compose's automatic discovery of the
override file, so Start-Codeman.sh silently ignored docker-compose.override.yml.
Any local customisation placed in the conventional override file was dropped
without warning, and the only way to notice was to inspect the running
container.

Collect the -f arguments into an array, append the override file when one is
present, and reuse that array for the final launch so the two cannot drift
apart again. Both .yml and .yaml are checked, in Compose's own precedence
order, and the chosen file is reported on startup.

Document the override file in docker/README.md, including the two things that
are easy to get wrong: it is ignored when -f is passed without naming it, and
it cannot remove a key such as ports, which Compose concatenates. Add the
override file to .gitignore.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitignore

@@ -48,6 +48,10 @@ Thumbs.db
 .env.local
 .env.*.local
 
+# Local Compose customisation (host-specific, not part of the project)
+docker-compose.override.yml
+docker-compose.override.yaml
+
 # State files (local to each machine)
 .claude/ralph-loop.local.md