Stopped the release script adding a Co-authored-by trailer (#777)

prepare_release.sh committed the version passes with a Co-authored-by trailer naming an
AI. That trailer asserts authorship an AI cannot hold: the human contributor signs the
ECA and is solely responsible for the contribution. It is already in the published
history, on the 6.5.1.202602 and 6.5.1.202602a preparations.

The commits now carry their subject alone. A version pass is mechanical sed output, so
no agent produces it at run time; an agent that runs the script records its own
Assisted-by trailer on that run instead. The script also gains the AI disclosure line it
was missing.

Ran the patched script against a scratch clone targeting 6.5.2.202603. Both commits come
out with an empty trailer block, the version constants and 211 port version strings
update as before, and check_ports.sh passes.

Assisted-by: Claude Code (Opus 5) <noreply@anthropic.com>

scripts/prepare_release.sh

@@ -15,6 +15,7 @@
 #
 # Copyright (C) 2026 Eclipse ThreadX contributors
 # SPDX-License-Identifier: MIT
+# Portions of this file were generated with AI assistance.
 
 set -eu
 
@@ -134,8 +135,6 @@ sed -i -E "s|(#define THREADX_HOTFIX_VERSION[[:space:]]+)'[^']*'|\1${HOTFIX_DEFI
 git -C "${REPO_ROOT}" add "${API_HEADER}"
 git -C "${REPO_ROOT}" commit -F - <<'COMMIT_EOF'
 Updated version number constants
-
-Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
 COMMIT_EOF
 
 printf "Committed version constant updates.\n"
@@ -175,8 +174,6 @@ EOF
     else
         git -C "${REPO_ROOT}" commit -F - <<'COMMIT_EOF'
 Updated port version strings
-
-Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
 COMMIT_EOF
         printf "Committed port version string updates.\n"
     fi