load_measurements() (DB path) patches missing station-hours from the
hii_waterlevel mirror telemetry: exact mirrors (P.1/P.103/P.20/P.4A/P.67/
P.75/P.82/P.84/P.92) plus bias-corrected P.81 (+9,340 h). Per-station
MSL->gauge offset is derived from >=168 h of series overlap, which
reproduces the published offsets for exact mirrors and absorbs P.81's
bias; P.76/P.77/P.85/P.87 HII twins are different physical sensors and
stay excluded. Training and serving share the loader, so both sides see
identical filled series; water_measurements is never written.
