feat: add bounded fleet summary

[andrei-hasna]

Summary

• add dispatch fleet summary, SDK support, and MCP dispatch_fleet_summary with schemaVersion dispatch.fleet_summary.v1
• classify bounded tmux panes as working, idle, stuck, error, or blocked with uncertainty and redacted excerpts
• add AI provider preflight and bound existing dispatch targets --json output by default, with --all as explicit full-enumeration opt-in

Validation

• bun run typecheck
• bun test (411 pass)
• bun run build
• local smoke: fleet summary --targets '*' --limit 2 --max-pane-chars 300 --json
• cross-machine smoke: fleet summary --machine spark01 --targets '*' --limit 1 --max-pane-chars 200 --json
• preflight smoke: fleet summary --preflight-ai --provider none --json exits 1 with failed JSON and inspectedTargets=0

Todo: 525c99fc-b414-41f9-a6a2-721e3510ce82