Normalized the AI disclosure comment to one fixed line per file (#740)

The per-edit disclosure named the product and model, so every agent and every
model version appended another line. 74 files carried two to four of them, and
the same five products had accumulated 13 spellings -- Copilot against GitHub
Copilot, Claude Sonnet 4.6 against claude-sonnet-4.6, four spellings of Codex.
Twenty assembly lines carried a doubled comment marker, `; //` or `@ //`.

Every file now carries exactly one line, fixed text naming no product:

    Portions of this file were generated with AI assistance.

It is written with the comment character that file already uses, so the `;`
and `@` assembly files keep theirs and the doubled markers are gone. Precise
attribution stays on the commit, where the Assisted-by trailer is per-change,
dated and attached to the diff it describes. A header line cannot hold that
record honestly, because the code it names gets rewritten and the line stays.
A file-level flag answers whether; the history answers who.

Comment-only. 455 files, 455 insertions and 574 deletions: every removed line
was a disclosure line, every added line is the fixed text, and no file is left
with zero or with more than one. `scripts/check_ports.sh` passes, including the
reproducibility check that would catch a ports_arch master and its generated
copies drifting apart. Recompiled against dev, every file that builds without a
vendor toolchain gives a byte-identical object: 19 of 19 C files under common,
100 of 100 GNU assembly files, and all 16 assemblable files whose comment
marker changed. The 10 remaining marker changes are ac5 and IAR sources where
`;` already started the comment and only the redundant `//` was removed.

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

common_modules/inc/txm_module.h

@@ -9,7 +9,7 @@
  * SPDX-License-Identifier: MIT
  **************************************************************************/
 
-// Some portions generated by Copilot (Opus 5).
+// Portions of this file were generated with AI assistance.
 
 
 /**************************************************************************/

common_modules/module_manager/inc/txm_module_manager_dispatch.h

@@ -8,8 +8,7 @@
  *
  * SPDX-License-Identifier: MIT
  **************************************************************************/
-// Some portions generated by Codex (GPT-5).
-// Some portions generated by Copilot (Opus 5).
+// Portions of this file were generated with AI assistance.
 
 
 /**************************************************************************/

common_modules/module_manager/src/txm_module_manager_absolute_load.c

@@ -9,7 +9,7 @@
  * SPDX-License-Identifier: MIT
  **************************************************************************/
 
-// Some portions generated by Copilot (Opus 5).
+// Portions of this file were generated with AI assistance.
 
 
 /**************************************************************************/

common_modules/module_manager/src/txm_module_manager_absolute_load_extended.c

@@ -9,7 +9,7 @@
  * SPDX-License-Identifier: MIT
  **************************************************************************/
 
-// Some portions generated by Copilot (Opus 5).
+// Portions of this file were generated with AI assistance.
 
 
 /**************************************************************************/

common_modules/module_manager/src/txm_module_manager_thread_create.c

@@ -9,7 +9,7 @@
  * SPDX-License-Identifier: MIT
  **************************************************************************/
 
-// Some portions generated by Copilot (Opus 5).
+// Portions of this file were generated with AI assistance.
 
 
 /**************************************************************************/

common_modules/module_manager/utilities/module_binary_to_c_array.c

@@ -9,7 +9,7 @@
 /* SPDX-License-Identifier: MIT                                            */
 /***************************************************************************/
 
-// Some portions generated by Claude Code (Opus 5)
+// Portions of this file were generated with AI assistance.
 
 #include <stdio.h>
 #include <stdlib.h>

common_modules/module_manager/utilities/module_to_binary.c

@@ -9,7 +9,7 @@
 /* SPDX-License-Identifier: MIT                                            */
 /***************************************************************************/
 
-// Some portions generated by Claude Code (Opus 5)
+// Portions of this file were generated with AI assistance.
 
 #include <stdio.h>
 #include <stdlib.h>

common_modules/module_manager/utilities/module_to_c_array.c

@@ -9,7 +9,7 @@
 /* SPDX-License-Identifier: MIT                                            */
 /***************************************************************************/
 
-// Some portions generated by Claude Code (Opus 5)
+// Portions of this file were generated with AI assistance.
 
 #include <stdio.h>
 #include <stdlib.h>