feat: add Amp SDK configuration to ralph-starter config and CLI flags

[rubenmarcus]

Summary

Add Amp-specific configuration options and CLI flags to ralph-starter.

Linear: ENG-1465

CLI Changes

ralph-starter run --agent amp --from github --issue 42
ralph-starter run --agent amp --amp-mode smart  # or rush, deep
ralph-starter run --agent amp --amp-mode rush   # fast mode

Amp Agent Modes

• smart: Unconstrained frontier models (best quality, slower)
• rush: Fast/efficient mode (quick iterations)
• deep: Extended reasoning (complex problems)

Config File

# ralph.config.yml
agent: amp
amp:
  mode: smart
  # other Amp-specific options

Files

• src/commands/run.ts (CLI flags)
• src/config.ts (config schema)
• src/loop/agents.ts (Amp config mapping)

Depends On

• Issue K (Research)
• Issue L (Agent abstraction)