feat(local-identity): add --username and --fullname overrides to init

Resolves the system identity mismatch between the Linux username (worsch)
and the bootstrap identity (tegwick / Bernd Worsch / custom email).

Resolution order for all three fields: flag > config > system derivation.
Config is updated on every init so --force reinits are idempotent without
repeating the flags.

- cli.py: extract _resolve_init_params(); add --username / --fullname args;
  persist all three fields to config.yaml on init
- tests/test_cli.py: 13 new tests covering flag priority, config fallback,
  system derivation, config persistence, idempotent --force reinit

54 tests passing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

local-identity/src/local_identity/cli.py

@@ -2,8 +2,10 @@
 local-identity CLI — entry point.
 
 Commands:
-  init [--force] [--email EMAIL]   Derive primary user from Linux identity,
-                                   generate test users, write store.
+  init [--force] [--username U] [--fullname N] [--email E]
+                                   Derive primary user, generate test users,
+                                   write store.  All three identity fields are
+                                   resolved flag > config > system derivation.
   list                             List all users in the store.
   show <username>                  Display a user's YAML record.
 
@@ -19,6 +21,20 @@ from .user import UserRecord, make_test_user
 from . import store
 
 
+def _resolve_init_params(args: argparse.Namespace, config: dict) -> tuple[str, str, str]:
+    """
+    Resolve (username, fullname, email) for init from three sources in order:
+      1. CLI flags (--username, --fullname, --email)
+      2. Persisted config (~/.local-identity/config.yaml)
+      3. System derivation ($USER / /etc/passwd GECOS) — username + fullname only
+         Email has no system default; missing email falls through to prompt in cmd_init.
+    """
+    username: str = args.username or config.get("username") or current_username()
+    fullname: str = args.fullname or config.get("fullname") or get_gecos_fullname(username)
+    email: str = args.email or config.get("email") or ""
+    return username, fullname, email
+
+
 def cmd_init(args: argparse.Namespace) -> None:
     if store.store_exists() and not args.force:
         print(
@@ -28,12 +44,9 @@ def cmd_init(args: argparse.Namespace) -> None:
         )
         sys.exit(1)
 
-    username = current_username()
-    fullname = get_gecos_fullname(username)
-
-    # Email resolution: flag > existing config > interactive prompt
     config = store.read_config() if store.store_exists() else {}
-    email: str = args.email or config.get("email", "")
+    username, fullname, email = _resolve_init_params(args, config)
+
     if not email:
         try:
             email = input(f"Email address for {username}: ").strip()
@@ -44,7 +57,7 @@ def cmd_init(args: argparse.Namespace) -> None:
             sys.exit(1)
 
     store.init_dirs()
-    config["email"] = email
+    config.update({"username": username, "fullname": fullname, "email": email})
     store.write_config(config)
 
     primary = UserRecord(username=username, fullname=fullname, email=email)
@@ -102,9 +115,17 @@ def main() -> None:
         "--force", action="store_true",
         help="Reinitialise even if the store already exists",
     )
+    p_init.add_argument(
+        "--username",
+        help="Bootstrap username (default: $USER / $LOGNAME)",
+    )
+    p_init.add_argument(
+        "--fullname",
+        help="Full display name (default: /etc/passwd GECOS field)",
+    )
     p_init.add_argument(
         "--email",
-        help="Email address (skips interactive prompt)",
+        help="Email address (default: interactive prompt)",
     )
     p_init.set_defaults(func=cmd_init)