PR template duplicates the commit message and needs edits to fill in

Problem:  The PR template asks again for what the commit message
          already provides as the title and description, and its
          checklist items list alternatives in one line that must be
          edited instead of ticked.  AGENTS.md shows a patch number in
          the subject, which is added only when merging.
Solution: Explain the commit message form in a comment, give each
          alternative its own checkbox, and drop the patch number from
          the AGENTS.md example.

closes: #21454

Assisted-by: Claude
Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

.github/pull_request_template.md

@@ -3,50 +3,35 @@ Thanks for contributing to Vim!
 
 Please read CONTRIBUTING.md if you have not already.  The comments below
 are not shown in the pull request; delete any section that does not apply.
+
+Write the commit message in this form:
+
+    Short description of the problem
+
+    Problem:  One sentence: what is wrong, from the user's point of view.
+    Solution: One sentence: what this change does about it (Your Name).
+
+    Anything longer (mechanism, benchmark numbers, why an alternative
+    was rejected) goes here.
+
+    fixes:   #number
+    related: #number
+
+For a pull request with a single commit, GitHub uses the first line as
+the title and the rest as the start of this description.
+
+For changes to runtime files the first line starts with one of:
+
+    runtime(doc): for a documentation update
+    translation(isocode): translations into language
+    runtime(lang): runtime file changes for language lang
+    filetype: for changes to filetype detection
+
+Add "fixes: #number" when this fixes a reported issue, and
+"related: #number" when it references another issue or pull request.
+"closes: #number" is added when merging.
 -->
 
-### What does this change do?
-
-<!--
-In one or two sentences, please clearly write what problem this PR fixes.
-For visual changes, a before/after screenshot is helpful.
--->
-
-### Commit message
-
-<!--
-Changes to the C core are merged with a message in this form.
-
-    Problem:  <one short sentence: what is wrong, from the user's point of view>
-    Solution: <one short sentence: what this does about it> (Your Name).
-
-Anything longer (mechanism, benchmark numbers, why an alternative was
-rejected) goes in the body below the Solution line.
-
-Align the Problem and Solution lines.
-
-Changes to runtime files use the following form:
-
-runtime(doc): for a documentation update
-translation(isocode): translations into language
-runtime(lang): runtime file changes for language lang
-filetype: for changes to filetype detection
--->
-
-    Problem:  Problem line
-    Solution: Solution line (Your Name).
-
-<!--
-If this PR references a previously merged one, add a related: #number
-If this PR fixes a reported issue, add a fixes: #number
-Keep the closes: header; it is filled in when the PR is merged
-
-Align the # columns
--->
-related: #number
-fixes:   #number
-closes:  #number
-
 ### AI assistance
 
 <!--
@@ -54,14 +39,24 @@ Please disclose AI involvement by adding the trailer
   "Assisted-by: AI tool".
 -->
 
-- [ ] AI involvement is disclosed in the commit message, or no AI was used
+- [ ] AI involvement is disclosed in the commit message
+- [ ] No AI was used
 
 ### Checklist
 
 - [ ] The commit message follows the Problem/Solution form above
 - [ ] `Signed-off-by:` trailer is present (`git commit -s`), recommended but not required
-- [ ] Tests were added, existing tests cover the change, or the change cannot be tested (say why)
-- [ ] Documentation under `runtime/doc/` was updated, or no update is needed
+
+#### Tests
+
+- [ ] Tests were added
+- [ ] Existing tests cover the change
+- [ ] The change cannot be tested (explain below)
+
+#### Documentation
+
+- [ ] Documentation under `runtime/doc/` was updated
+- [ ] No documentation update is needed
 
 ### Anything reviewers should know
 

AGENTS.md

@@ -74,7 +74,7 @@ Before submitting any patch, at minimum:
 Vim uses a strict commit message format. The subject line is a
 one-sentence **problem statement**, not a description of the fix:
 
-    patch 9.2.NNNN: short description of the problem
+    short description of the problem
 
     Problem:  Restatement of the problem as a full sentence, possibly
               with a reporter attribution in parentheses.