feat(default-mode): auto-activate ultrawork and ralph loop without commands

Add new `default_mode` config section with two boolean fields:
- `ultrawork`: Auto-inject ultrawork mode prompt on main session start
  without requiring the "ultrawork"/"ulw" keyword. Wired through the
  keyword-detector hook — injects once per session, respects existing
  guards (non-OMO agents, planner agents, subagent sessions).
- `ralph_loop`: Auto-start ralph loop on first main session message
  without requiring /ralph-loop or /ulw-loop commands. When ultrawork
  is also enabled, the loop starts in ultrawork mode.

Usage:
  ```jsonc
  {
    "default_mode": {
      "ultrawork": true,    // Always get ultrawork prompt on start
      "ralph_loop": true    // Auto-start ralph loop
    }
  }
  ```

Files: 7 modified/added, ~65 LOC added.

src/config/schema.ts

@@ -7,6 +7,7 @@ export * from "./schema/categories"
 export * from "./schema/claude-code"
 export * from "./schema/comment-checker"
 export * from "./schema/commands"
+export * from "./schema/default-mode"
 export * from "./schema/dynamic-context-pruning"
 export * from "./schema/experimental"
 export * from "./schema/fallback-models"