Add per-phase timeouts to Coder subagent

Currently there's one timeout for the whole coder run (default 600s). Long verify phases can eat into work time unpredictably.

Add separate timeouts:

• Init phase: 30 seconds (git pull, initial build check)
• Work loop: configurable, main budget
• Verify phase: 120 seconds per attempt (lint, typecheck, build, test)

This gives better predictability and prevents a slow test suite from consuming the entire budget.