Let config.env preset the project details

Eight optional keys (PROJECT_NAME, PROJECT_DESCRIPTION, PROJECT_VISIBILITY,
GITEA_OWNER, USE_GITHUB, GITHUB_OWNER, PROJECT_DIRECTORY, ENABLE_PLAN_GATE)
are read and checked with the validators the prompts use. A key that is
present counts as set (only the description may be empty); it is not asked
and the summary marks it "(from config.env)". An invalid value stops the
run before any request and names the key. USE_GITHUB=no skips the GitHub
owner and warns about a stray GITHUB_OWNER. The confirmations stay
interactive. Keys and an example are documented; tests cover every key.

Task: MIL-004#1
Task: MIL-004#2
Task: MIL-004#3
Task: MIL-004#4
Task: MIL-004#5
Closes #27
Closes #28
Closes #29
Closes #30
Closes #31

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

config.env.example

@@ -30,6 +30,21 @@ GITEA_API_URL=https://<your gitea instance>/api/v1
 # The server may enforce a minimum. Default: 10m0s.
 #MIRROR_INTERVAL=10m0s
 
+# Optional. Project details that are set here are not asked. A key that is
+# present counts as set, even when empty; only PROJECT_DESCRIPTION may be
+# empty. An invalid value stops the run and names the key. Remove or comment
+# out a line to be asked for it. The confirmations ("Create these now" and
+# the questions about existing repositories, directories and files) are
+# always asked.
+#PROJECT_NAME=my-project
+#PROJECT_DESCRIPTION=What the project is for
+#PROJECT_VISIBILITY=private            # private or public
+#GITEA_OWNER=my-organization
+#USE_GITHUB=yes                        # yes or no
+#GITHUB_OWNER=my-organization          # used only when USE_GITHUB is yes
+#PROJECT_DIRECTORY=./my-project
+#ENABLE_PLAN_GATE=no                   # yes or no
+
 # Optional. OWNER/NAME of the SQA-QC-Framework repository on the Gitea server;
 # it is added to the new project as a submodule over SSH.
 # Default: TirSystem/SQA-QC-Framework.