fix: resolve three bugs flagged by Greptile on PR #22894

1. .gitignore: replace blanket `.claude` exclusion + broken `!.claude/commands`
   negation with specific exclusions. Git cannot re-include files inside a
   fully-excluded parent directory, so the negation had no effect and the
   command files were never tracked.

2. error_related_to_PR.md: replace literal `[PR_NUMBER]` placeholder with
   `$ARGUMENTS[0]` so the command actually uses the supplied argument.

3. deletable_PR_argument.md: fix `$ARGUMENT[0]` (singular, non-standard) →
   `$ARGUMENTS[0]` (plural, Claude Code convention).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/commands/deletable_PR_argument.md

@@ -1,6 +1,6 @@
 This is a table of PRs
 
-$ARGUMENT[0]
+$ARGUMENTS[0]
 
 from the above table,
 for each row,

.claude/commands/error_related_to_PR.md

@@ -1,6 +1,6 @@
 Let the value for PR Number equals to $ARGUMENTS[0]
 
-Is this related to my PR [PR_NUMBER]? if yes, fix it; else, create a new PR fixing the issue. Is very IMPORTANT that the PR be as scoped as possible, just touching relevant files that fix the issue, and if required create the fix from the main branch, not just from the PR branch contents: this will guarantee consistency and fixing the error in general.
+Is this related to my PR $ARGUMENTS[0]? if yes, fix it; else, create a new PR fixing the issue. Is very IMPORTANT that the PR be as scoped as possible, just touching relevant files that fix the issue, and if required create the fix from the main branch, not just from the PR branch contents: this will guarantee consistency and fixing the error in general.
 
 The error found is:
 

.gitignore

@@ -2,8 +2,8 @@
 .venv
 .venv_policy_test
 .env
-.claude
-!.claude/commands
+.claude/settings.local.json
+.claude/__pycache__
 .newenv
 newenv/*
 litellm/proxy/myenv/*