feat(docker): guided first run for the Compose deployment

A new Docker install was: clone (undocumented), copy .env.example by hand,
fix an Unraid data path and a Perth time zone, replace `changeme`, run the
start script, and then guess when the server was up. Start-Codeman.sh now
does all of it from a fresh clone:

- Preflight names the fix for a missing docker CLI, a missing or too-old
  Compose plugin (config --environment needs 2.27.2, docker/compose#11891),
  and an unreachable daemon (docker group, never sudo).
- With no docker/.env, it asks three questions (data folder, port,
  password; Enter takes each default: ~/codeman-docker, 3000 or the next
  free port, a generated password) and writes docker/.env FROM the example,
  so every key the updater's diffRequiredEnvKeys expects is present. Mode
  0600, host time zone, values Compose would interpolate single-quoted.
  Refuses $HOME, ~/.codeman (a native install's state dir) and anything
  inside the checkout (the image build context). --yes / no TTY take the
  defaults, --setup-only stops after writing the file. An existing .env is
  never edited, and root never runs the setup (Unraid keeps the hand route).
- After `up`, it waits until the server answers (docker exec probe, crash
  loop caught by the restart count) and prints the URL, the LAN URL, the
  generated password and the logs/stop commands; --no-wait skips the wait.
- `changeme` is refused before anything starts (the container publishes on
  every interface and holds the Docker socket); Update-Codeman.sh checks it
  before its build and down so the stack is never left stopped.
- Compose settings are read with ONE config --environment call, with its
  error reported, instead of three silent ones.

docker-compose.yaml and server.Dockerfile are untouched (their hashes gate
the in-app updater), and .env.example changes values and comments only.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docker/.env.example

@@ -1,9 +1,14 @@
 # =============================================================================
 # Codeman Docker Compose environment template
-# Copy this file to .env and set the values for the Docker host.
+#
+# Usually there is no need to copy this by hand: on its first run,
+# `bash docker/Start-Codeman.sh` writes docker/.env from this file, asking for
+# the data folder, port and password and filling in this host's time zone.
+# Copy it yourself (to docker/.env) only for a hand-built setup, such as a host
+# where everything runs as root (Unraid) or Compose started without the script.
 # =============================================================================
 
-TZ=Australia/Perth
+TZ=Etc/UTC
 
 # Optional overrides for direct `docker compose` use. The Bash start script
 # detects these values from CODEMAN_APPDATA_PATH automatically. Compose uses
@@ -23,7 +28,8 @@ CODEMAN_RUNTIME_USER=codeman
 
 # Required. Persistent Codeman application data, CLI credentials, and session
 # state are stored here on the host and mounted at the runtime account's home
-# directory in the container.
+# directory in the container. The value below is the Unraid layout; the first
+# run of Start-Codeman.sh suggests ~/codeman-docker instead.
 CODEMAN_APPDATA_PATH=/mnt/user/appdata/codeman
 
 # Optional. Absolute host path of this Codeman checkout, mounted at
@@ -45,6 +51,7 @@ CODEMAN_IMAGE=codeman:local
 
 # Required for any network-accessible Codeman instance. Use a unique, strong
 # password. This file is safe to commit; copy it to .env and set the value.
+# Start-Codeman.sh refuses to start while it is still `changeme`.
 CODEMAN_PASSWORD=changeme
 
 # Required. Username for Codeman HTTP Basic authentication.