Migrate the remaining simple timers

• Status: Done
• Kind: Feature
• Authors: Jean Mertz git@jeanmertz.com
• Date: 2026-08-27
• Implements: 091

Migrates the reasoning timer, lock-wait countdown, MCP startup timer, both drain timers, and the stream-retry notice to the printer, and moves the lock-contention prompt from err_writer() to prompt_writer(). Deletes spawn_line_timer and LineTimer; the retry notice keeps its non-terminal branch and retry_tests coverage.