fix: Prevent bot self-trigger infinite loops in all workflows

CRITICAL FIX: Bot was triggering itself causing 10+ duplicate runs

Problem:
- When bot posts comments containing @codebot (e.g., help responses, PR reviews)
- Workflows trigger on those bot comments
- Bot responds again with @codebot mention
- Infinite loop → 10+ duplicate workflow runs → excessive API costs

Solution:
- Added github.event.comment.user.login != 'Bartender' to all workflow conditions
- Prevents bot from reacting to its own comments
- Bot username 'Bartender' is now hardcoded in workflows

Changes:
- .gitea/workflows/ai-comment-reply.yml: Added bot username check
- .gitea/workflows/ai-chat.yml: Added bot username check
- .gitea/workflows/ai-issue-triage.yml: Added bot username check
- CLAUDE.md: Documented bot self-trigger prevention and username update instructions
- README.md: Added Step 3 to bot customization with critical warning

Impact:
- Eliminates infinite loop scenarios
- Prevents excessive API costs from duplicate runs
- Workflows only trigger on human user comments

Note: If bot username changes from 'Bartender', all three workflow files must be updated.

README.md

@@ -479,6 +479,15 @@ if: contains(github.event.comment.body, '@codebot')
 
 Change `@codebot` to your new bot name.
 
+**Step 3 (CRITICAL):** Update bot username to prevent infinite loops:
+
+In all three workflow files, find:
+```yaml
+github.event.comment.user.login != 'Bartender'
+```
+
+Replace `'Bartender'` with your bot's Gitea username. This prevents the bot from triggering itself when it posts comments containing `@codebot`, which would cause infinite loops and 10+ duplicate workflow runs.
+
 ---
 
 ## Security Scanning