Remove duplicate agent routing skills

[fredporter]

Summary

• remove the deprecated route_task compatibility shim
• remove hard-coded HiveMind consensus and Roundtable dispatch Skill wrappers
• keep Flow Router as the single provider and budget routing path
• remove the workflow seed that depended on the retired shim and align the Skills audit

Verification

• 486 backend tests passed
• changed-file Ruff checks passed
• git diff --check passed

Notes

• HiveMind service remains intact behind its existing API
• repository-wide Ruff still contains pre-existing findings outside this slice