Renumber the six VCS migrations off the 213/214/215 prefix collisions to a unique contiguous tail 216-221 (tables before indexes), and make 214_chat_session_project idempotent (ADD COLUMN IF NOT EXISTS) so the #5868 rename-induced re-run no-ops instead of crashing. Fixes the red migration lint on main and unblocks the dev deploy.
PR #5765 (MUL-5150) branched before #5841 merged, so both landed a 213
migration and Backend CI's TestMigrationNumericPrefixesStayUniqueAfterLegacySet
failed on main. Bump #5765's pair to the next free prefixes, preserving the
column-before-index order:
213_chat_session_project -> 214_chat_session_project
214_chat_session_project_index -> 215_chat_session_project_index
MUL-5251
Co-authored-by: Bohan-J <bohan@devv.ai>
Co-authored-by: multica-agent <github@multica.ai>
