fix: enable block streaming for Telegram when streamMode is 'block'

- Fix disableBlockStreaming logic in telegram/bot.ts to properly enable
  block streaming when telegram.streamMode is 'block' regardless of
  blockStreamingDefault setting
- Set minChars default to 1 for Telegram block mode so chunks send
  immediately on newlines/sentences instead of waiting for 800 chars
- Skip coalescing for Telegram block mode when not explicitly configured
  to reduce chunk batching delays
- Fix newline preference to wait for actual newlines instead of breaking
  on any whitespace when buffer is under maxChars

Fixes issue where all Telegram messages were batched into one message
at the end instead of streaming as separate messages during generation.

src/agents/pi-embedded-block-chunker.ts

@@ -221,6 +221,10 @@ export class EmbeddedBlockChunker {
       if (sentenceIdx >= minChars) return { index: sentenceIdx };
     }
 
+    if (preference === "newline" && buffer.length < maxChars) {
+      return { index: -1 };
+    }
+
     for (let i = window.length - 1; i >= minChars; i--) {
       if (/\s/.test(window[i]) && isSafeFenceBreak(fenceSpans, i)) {
         return { index: i };