fix(studio): improve chat context, thinking tags, streaming, and tool results

- Fix cleanThinkingTags to use proper regex instead of naive ReplaceAll
- Send conversation history (last 20 messages + summary) to AI instead of single message
- Store tool results alongside tool calls so history shows complete execution info
- Stream words instead of characters for smoother SSE rendering
- Add stop button to cancel in-progress AI requests (AbortController)
- Fix markdown rendering: add h2 support, use div for bullets
- Add i18n keys for cancel/stop (EN + FR)

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

web/src/i18n/fr.js

@@ -90,6 +90,8 @@ const fr = {
     you: 'Vous',
     mentioned: 'mentionn\u00e9',
     cleared: 'Conversation effac\u00e9e.',
+    cancelled: 'Requ\u00eate annul\u00e9e.',
+    stop: 'Stop',
   },
 
   shell: {