docs+infra: reposition the README, add a runnable demo, disarm the migration flag

README now leads with the cross-teammate wedge and tells single-developer users
to use Agent Teams, which is both true and the only honest way to sell against a
free platform default. Feature list rewritten to state what is actually
guaranteed (SKIP LOCKED claims, tamper-evident locks) instead of "distributed
shared memory" and "high-fidelity mirroring".

Adds examples/two-agent-collision.ts: a runnable, fully offline demo that shows
one agent granted, a second told who holds the file and why, then routed onto
another job. Every status it prints is a real return value. It forces local-only
persistence, because on first run it happily connected to the live Supabase and
the real org.

Removes --include-all from migrate.yml. Production has no schema_migrations rows
for 0000-0007, so the flag replays 0007, whose cochange_neighbors returns four
columns where prod already has the five-column 0012 version. CREATE OR REPLACE
across a changed return type aborts the whole push. The commit that added the
flag documented this hazard and shipped it anyway; the manual repair command is
now in the workflow comment and supabase/README.

Adds server.json for the official MCP registry. Untracks tests/load-test-state.json,
a runtime artifact that CI's own load test rewrites, dirtying the tree on every run.