Fix proposal naming validation to only check new files (#2788)

The --diff-filter option was missing the equals sign, which could cause
git to misinterpret 'A' as a path argument instead of the filter value.
This resulted in the validation failing even when only updating existing
proposal files.

Changes:
- Fix --diff-filter syntax from '--diff-filter A' to '--diff-filter=A'
- Add '|| true' to grep to handle cases with no matching files
- Update comments to clarify the intent

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: JAORMX

.github/workflows/validate-proposal-naming.yml

@@ -37,12 +37,13 @@ jobs:
 
       - name: Validate proposal naming
         run: |
-          # Get the list of changed files in docs/proposals
-          CHANGED_FILES=$(git diff --name-only --diff-filter A origin/${{ github.base_ref }}...HEAD | grep '^docs/proposals/')
+          # Get the list of NEW files added in docs/proposals (not modifications to existing files)
+          CHANGED_FILES=$(git diff --name-only --diff-filter=A origin/${{ github.base_ref }}...HEAD | grep '^docs/proposals/' || true)
 
-          # This is here to avoid errors when running this workflow manually without a PR
+          # Skip validation if no new proposal files are being added
+          # (modifications to existing proposals don't need naming validation)
           if [ -z "$CHANGED_FILES" ]; then
-            echo "ℹ️ No proposal files changed in this PR"
+            echo "ℹ️ No new proposal files added in this PR (only modifications to existing proposals or manual trigger)"
             exit 0
           fi