codex: persistent mcp-server driver + global config fix

- New CodexDriver (codex-driver.ts): spawns `codex mcp-server` as a
  long-running child process, drives multi-turn conversations via MCP
  JSON-RPC protocol using `codex` (start) and `codex-reply` (continue)
  tools. Replaces single-shot `codex exec` which exited after one turn.

- Launcher: Codex agents now use CodexDriver instead of `codex exec`.
  The driver stays alive between turns, maintaining full thread history.
  Orchestrator pushes teammate messages as new turns via driver.reply().

- Orchestrator: added message forwarding loop (3s interval) that polls
  broker for undelivered messages to Codex slots, formats them, and
  pushes as new codex-reply turns. Codex is now reactive to teammates.

- Global config fix: ensureMcpConfigs writes to ~/.codex/config.toml
  (global) instead of project-level .codex/config.toml which Codex
  ignores. Removed broken `-c mcp_servers.*` CLI overrides that Codex
  silently drops. Fixed TOML section regex for values containing `[`.

- Tests updated for new Codex behavior (94/94 passing).