#11445: feat: enable block streaming by default, default break to message_end

## What 1. Changes the default value of `blockStreamingDefault` from `"off"` to `"on"`. 2. Changes the default value of `blockStreamingBreak` from `"text_end"` to `"message_end"`. ## Why **Block streaming on by default:** When block streaming is off (current default), users on messaging channels (Telegram, Discord, etc.) see **no output** during long multi-step agent tasks until the entire turn completes. With block streaming on, text blocks are sent progressively, giving users real-time visibility. **message_end as default break:** With `text_end`, messages split prematurely whenever tool calls happen mid-reply -- the text before a tool call gets flushed as a separate message, resulting in fragmented replies. `message_end` waits for the complete assistant turn, delivering clean single messages. ## Changes - `src/auto-reply/reply/get-reply-directives.ts`: Flip defaults so unset `blockStreamingDefault` resolves to `"on"` and unset `blockStreamingBreak` resolves to `"message_end"` - `src/config/types.agent-defaults.ts`: Update JSDoc to reflect new defaults ## Backward compatibility Users who prefer the old behavior can explicitly set `blockStreamingDefault: "off"` and/or `blockStreamingBreak: "text_end"` in their config. No breaking changes -- existing configs with explicit values are unaffected.