feat!: AI wrappers always send through capture_ai

[eli-r-ph]

💡 Motivation and Context

Stacked on #1026. AI wrapper events went to the analytics endpoint unless enable_full_ai_capture was set, and that endpoint caps an event near 1 MB. The AI endpoint accepts up to 8 MiB, but reaching it also meant turning off truncation and media redaction. This PR always sends wrapper events through capture_ai, and enable_full_ai_capture now controls content only.

Changes

• The OpenAI, Anthropic, Gemini, LangChain, Claude Agent SDK and OpenAI Agents integrations always use capture_ai, through one helper.
• A client object without capture_ai still receives capture calls.
• The deprecated _use_ai_lane and _enable_multimodal_capture aliases keep working.
• MCP events stay on capture, because they are not $ai_* events.

Warning

• Tests that assert on mock.capture for a wrapper now see mock.capture_ai.
• A deployment that does not serve /i/v1/ai/events now drops wrapper events.

This differs from the sdk-specs capture-ai spec, which ties routing to the flag; a spec change is still to be proposed.

💚 How did you test it?

• Every wrapper suite now asserts on capture_ai with the flag off.
• A real-client test checks that wrapper events reach only the AI endpoint, with the flag off and on.
• Restoring the old flag gate fails 311 tests.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Written with Cursor (Claude Opus) under the direction of the assignee.

🤖 Generated with Claude Code

[eli-r-ph]

@greptileai review