[Docs] Prevent MDL codes in comments

- Replaced the permissive "feel free to include MDL-12345" guidance with an explicit guidance not to use  MDL codes in standard inline comments.
- Tightened the TODO section: added "A TODO without an MDL code is invalid." to track the work that still needs to be done.

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: ferranrecio

general/development/policies/codingstyle/index.md

@@ -1913,11 +1913,15 @@ function forum_get_ratings_mean($postid, $scale, $ratings = null) {
 
 </InvalidExample>
 
-If your comment is due to some MDL issue, please feel free to include the correct MDL-12345 in your comment. This makes it easier to track down decisions and discussions about things.
+:::note
+
+Do not include MDL issue codes in standard inline comments. Inline comments should explain the logic and purpose of the code, not historical tracker context.
+
+:::
 
 #### Using TODO
 
-This is especially important if you know an issue still exists in that code that should be dealt with later. Use a TODO along with a MDL code to mark this. For example:
+This is especially important if you know an issue still exists in that code that should be dealt with later. Use a TODO along with an MDL tracker reference to mark this. A TODO without an MDL tracker reference is invalid. For example:
 
 <ValidExample>
 

general/development/process/peer-review/index.md

@@ -208,6 +208,8 @@ Work does not stop when code is integrated.
 Ensure that:
 
 - The PHPdoc comments on all classes, methods and fields are useful. (Comments that just repeat the function name are not helpful! Add value.)
+- Standard inline comments do not include MDL tracker references and should focus on explaining logic and intent.
+- Every TODO comment includes a corresponding MDL issue code to track the work that still needs to be done.
 - Where an API has been changed significantly, ensure that [upgrade notes](../upgradenotes) have been written (or upgrade.txt on older branches).
 - Where something has been deprecated, that the comments don't just say "do NOT use this any more!!!" but actually follow the [deprecation policy](../../policies/deprecation/index.md).
 - Appropriate [labels](../../tracker/labels.md) have been added when there has been a function change, particularly