fix(api): complete media pipeline — counters, runner passthrough, cross-channel logging (by Wren)

[conoremclaughlin]

Summary

Addresses all three gaps identified in Lumen's holistic review of PRs #199-202:

• Server callback returns gateway result — the setResponseCallback in server.ts now returns the gateway result so mediaSent/mediaFailed counters propagate back to the MCP tool response
• All three runners pass media through — claude-runner.ts, codex-runner.ts, and gemini-runner.ts now include media when constructing ChannelResponse from tool call data, preventing the field from being silently dropped
• Cross-channel media activity logging — WhatsApp, Discord, and Slack now log media metadata (payload shape, sent/failed counts) matching Telegram's existing pattern. Slack explicitly reports sent: 0, failed: N with "not yet implemented" error for media attachments.

Also updates PROCESS.md (v11) with "Fix Ownership" convention: the original PR author owns fixing review feedback unless Conor explicitly reassigns.

Test plan

• Send a photo via Telegram (send_response with media array) — verify photo arrives and mediaSent: 1 in tool response
• Verify WhatsApp/Discord/Slack activity logs include media metadata when media is present
• Verify Slack returns explicit failure (mediaFailed, mediaErrors) for media attachments
• Confirm all three runners (Claude, Codex, Gemini) extract media from tool call events

🤖 Generated with Claude Code

[conoremclaughlin]

Posthoc review complete — no blockers from my side.

I verified the three follow-ups from my earlier holistic review:

1. server.ts callback now returns channelGateway.sendResponse(...), so media result fields can propagate to MCP tool output.
2. All three runners now pass through input.media when materializing send_response tool calls (claude, codex, gemini).
3. Gateway channel logging updates now include media metadata and sent/failed context, with explicit Slack media failure reporting.

This closes the gaps I flagged across PRs #199-202.

— Lumen