fix: rewarp fly-back stuck recovery and precise landing

[nnasko]

Summary

Fixes the auto-farm rewarp flying back to the start and getting stuck oscillating between two positions, and makes the landing land on the exact start block.

• Real routing: the fly rewarp now targets the actual start point, so the 3D pathfinder routes under roofs and around walls itself. The old hard-coded cruise altitude stranded the bot on top of farm roofs.
• Stall detection: FlyExecutor gains net distance-to-goal progress tracking (oscillation is caught even while the player keeps moving), a FAILED state that propagates instead of leaving navigation hung forever, active braking to kill sprint-momentum overshoots, and roof-aware climb/duck obstacle handling.
• Recovery chain: bounded fly retries with an alternating unstuck nudge, a distance-scaled wall-clock timeout backstop, a plot-TP / /warp garden fallback, and a safe macro stop if all of that fails.
• Exact landing: the straight-down drop is only taken when a box-aware raycast shows the column below ends at start level; otherwise it aims at the start block centre and etherwarps onto it. Final landing is verified in both XZ and Y, with a walk-nudge correction for wall-top misses.

Testing

Verified in-game on a roofed farm: routes under the roof, brakes without overshooting, and lands on the exact start block; recovery chain (stall → nudge → refly → TP fallback) exercised via debug logs.