feat: improve AI chat - system prompt, tool output, context window display (#17769)

⚠️ **AI-generated PR — not ready for review** ⚠️

cc @FelixMalfait

---

## Changes

### System prompt improvements
- Explicit skill-before-tools workflow to prevent the model from calling
tools without loading the matching skill first
- Data efficiency guidance (default small limits, use filters)
- Pluralized `load_skill` → `load_skills` for consistency with
`load_tools`

### Token usage reduction
- Output serialization layer: strips null/undefined/empty values from
tool results
- Lowered default `find_*` limit from 100 → 10, max from 1000 → 100

### System object tool generation
- System objects (calendar events, messages, etc.) now generate AI tools
- Only workflow-related and favorite-related objects are excluded

### Context window display fix
- **Bug**: UI compared cumulative tokens (sum of all turns) against
single-request context window → showed 100% after a few turns
- **Fix**: Track `conversationSize` (last step's `inputTokens`) which
represents the actual conversation history size sent to the model
- New `conversationSize` column on thread entity with migration

### Workspace AI instructions
- Support for custom workspace-level AI instructions

---------

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>

packages/twenty-server/src/engine/core-modules/twenty-config/config-variables.ts

@@ -1262,6 +1262,15 @@ export class ConfigVariables {
   @IsOptional()
   XAI_API_KEY: string;
 
+  @ConfigVariablesMetadata({
+    group: ConfigVariablesGroup.LLM,
+    isSensitive: true,
+    description: 'API key for Groq integration',
+    type: ConfigVariableType.STRING,
+  })
+  @IsOptional()
+  GROQ_API_KEY: string;
+
   @ConfigVariablesMetadata({
     group: ConfigVariablesGroup.SERVER_CONFIG,
     description: 'Enable or disable multi-workspace support',