Extract work graph service routes

[cbusillo]

Summary

• move work-graph snapshot/rank HTTP route wiring into control_plane/work_graph_http.py
• keep service.py responsible for app wiring while work-graph route auth/payload handling lives with the work graph boundary
• reduce control_plane/service.py to 7,711 lines in this slice

Refs #307

Validation

• uv run python -m unittest tests.test_service.LaunchplaneServiceTests.test_work_graph_rank_returns_ranked_queue tests.test_service.LaunchplaneServiceTests.test_work_graph_rank_rejects_unauthorized_identity tests.test_service.LaunchplaneServiceTests.test_work_graph_rank_rejects_unclassified_issue tests.test_service.LaunchplaneServiceTests.test_human_session_can_rank_work_graph_snapshot tests.test_service.LaunchplaneServiceTests.test_work_graph_snapshot_returns_launchplane_assembled_snapshot tests.test_service.LaunchplaneServiceTests.test_work_graph_snapshot_uses_compact_planning_facts_when_available tests.test_service.LaunchplaneServiceTests.test_work_graph_snapshot_rejects_unauthorized_identity tests.test_work_graph_service
• uv run --extra dev ruff check --diff control_plane/service.py control_plane/work_graph_http.py
• uv run --extra dev ruff check control_plane/service.py control_plane/work_graph_http.py
• uv run --extra dev mypy control_plane/service.py control_plane/work_graph_http.py