feat(thread): support persistent runtime and interaction modes

[tarik02]

Problem

start and send hardcode full-access and default, even though T3 Code stores runtime and interaction modes on each thread and exposes commands to change them.

Scope

• Add runtime and interaction mode flags to start, send, and thread update.
• Runtime mode values:
  • approval-required
  • auto-accept-edits
  • auto
  • full-access
• Interaction mode values:
  • default
  • plan
• Keep the current new-thread defaults when start flags are omitted.
• For send, inherit the thread's stored modes when flags are omitted.
• When send receives either flag, persist the supplied mode before starting the turn.
• Reject invalid mode values through typed CLI choices.

Acceptance criteria

• A mode set by send remains active for later turns.
• thread update can change either mode without sending a message.
• Supplying one mode leaves the other unchanged.
• The turn starts only after requested mode changes are accepted by the server.