Split agent_launch.rs and work_item_pipeline.rs to clear the LOC gate (#634)

Pure structural move via include!() — no logic changes. agent_launch.rs
tests moved to agent_launch_tests.rs; work_item_pipeline.rs split into
judge_decision.rs, prompt_builders.rs, and task_sourcing.rs. Unblocks #538's commit.

Agentflare-Agent: claude-code
Agentflare-Branch: task/542-split-agent-launch-rs-work-item-pipeline
Agentflare-Item: 542
Agentflare-Session: 13846c09-9c1f-4532-9028-cfa59a15a9d6

Author: getappz