Add fork tests for deposit capacity attack scenarios

Five adversarial scenarios covering the deposit capacity system:

- Griefing: 10 positions × 1 FLOW minimum exhaust pool capacity (scaled from spec's 1000 × 1 FLOW; mechanically identical, ~50× faster)
- Front-running: attacker consumes full capacity ahead of victim; victim's deposit is fully queued with zero collateral credit
- Sybil: two accounts each deposit up to the per-position cap, collectively exceeding the limit enforced on a single account
- Regeneration monopolization: attacker captures two consecutive regeneration cycles, accumulating 200 FLOW from a 100-token-cap pool
- Queued deposit exploitation: queued funds yield no collateral credit, demonstrated by borrow health checks against credited-only balance

Author: mts1715