fix(deploy): reference collector memory watermarks too small for current catalog

[proerror77]

Change contract

Production and shadow reference-collector units must not be throttled by cgroup memory.high during cold-start backfill at the current catalog size.

Production evidence (2026-08-01)

Shadow gate invocation 329edad2 (candidate 8cedff1c) failed: 'Rust shadow memory.events high grew or a MemoryMax/OOM event occurred'. The 672MiB/768MiB pair was calibrated in July for a smaller catalog; current state is 6509 tracked markets + 316k retained trade ids. Same defect class as the usdm archiver throttle stall (#534).

Acceptance

• Both units raised with measured justification in README calibration history
• control-plane/stage tests green
• Runtime: host drop-in already applied to the shadow template (documented in PR); production drop-in at cutover

Out of scope

• Collector memory reduction work