Desktop smoke-test of the rc.13 binary surfaced this: a Go int with omitempty can't tell
`pool: 0` from an omitted field, so `pool: 0` hit the `< 1` validation and rejected a
config that should have defaulted. Now pool 0/omitted → default 3; only a negative pool
errors. Added TestBalancerZeroPoolIsDefault; renamed the negative-pool test. SPEC_V2,
urltest.md, changelog rc.14 updated.
Verified on the rc.13 desktop binary: round_robin pool fill (pool_tolerance:0 tests only
pool-many nodes, >0 tests all), config fail-fast (balancer+least_test, unknown sticky_hash,
unknown mode, negative pool), and live routing through the group.