Remove the transition-era docs that no longer guide anyone and just pollute
context: MIGRATION-INVENTORY, CALLER-INVENTORY, GATE5-MIGRATION-GRAPH,
COLIBRI-CUTOVER-PLAN, and the rolling .agent-handoff.md. (History stays in git.)
Fix references in kept docs: drop the cutover/caller pointers (README,
COLIBRI-DAEMON-GLASSPANE-INTEGRATION), and repoint handoff mentions (AGENTS,
tools/README, MULTIAGENT-WORKFLOW-IMPROVEMENTS) to the ephemeral per-task
`doc/<FEATURE>-HANDOFF.md` convention. Dated session logs left as historical
record. Markdown gate green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
