feat(ai-chat): deferred tool loading (tiers + loadTools meta-tool) (#332)

The in-app AI agent shipped all ~41 tool schemas on every model step. This
adds a two-tier catalog: core tools (frequent or one-line) stay always-active;
the rest are advertised as a compact catalog and their full schema is fetched
on demand via the loadTools meta-tool, wired through ai@6 prepareStep's
per-step activeTools.

- tools/tool-tiers.ts: CORE_TOOL_KEYS, INLINE_TOOL_TIERS, applyLoadTools,
  catalog builders (+ tool-tiers.spec.ts, 13 cases).
- ai-chat.service.ts prepareAgentStep: returns activeTools =
  [...CORE_TOOL_KEYS, loadTools, ...activatedTools]; per-turn activated Set.
- ai-chat.prompt.ts: buildToolCatalogBlock renders the deferred catalog.
- mcp/tool-specs.ts: tier + catalogLine metadata (external snake_case /mcp
  transport unchanged).
- EnvironmentService.isAiChatDeferredToolsEnabled(): AI_CHAT_DEFERRED_TOOLS,
  default ON per issue intent (kill-switch =false restores old behavior).

Gate: server ai-chat 631/631, tool-tiers 13/13, mcp 472/472, tsc clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/server/src/integrations/environment/environment.service.ts

@@ -261,6 +261,21 @@ export class EnvironmentService {
     return disable === 'true';
   }
 
+  /**
+   * Deferred tool loading for the in-app AI chat (#332). When enabled, the agent
+   * sees a compact <tool_catalog> and only CORE tools + the loadTools meta-tool
+   * are active each step; deferred tools (the fat/rare ones + all external MCP
+   * tools) load on demand. Defaults to ENABLED — the issue treats deferred
+   * loading as the new behavior; set AI_CHAT_DEFERRED_TOOLS=false to restore the
+   * old "all tools always active" behavior.
+   */
+  isAiChatDeferredToolsEnabled(): boolean {
+    const enabled = this.configService
+      .get<string>('AI_CHAT_DEFERRED_TOOLS', 'true')
+      .toLowerCase();
+    return enabled === 'true';
+  }
+
   getPostHogHost(): string {
     return this.configService.get<string>('POSTHOG_HOST');
   }