feat: add <no-reply/> silent marker for agent opt-out (#196)

* feat: add {{NO_REPLY}} silent marker for agent opt-out

Allow the agent to respond with {{NO_REPLY}} to suppress message
delivery for messages that don't warrant a reply. The marker is
checked in three places: the streaming edit guard (prefix match to
prevent partial sends), finalizeMessage(), and the post-stream
response handler.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* refactor: use <no-reply/> XML marker instead of {{NO_REPLY}}

Switch to XML-style self-closing tag for consistency with the XML
envelope format used elsewhere, and because LLMs produce well-formed
XML tags more reliably than template syntax.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add no-reply hint to group chat envelopes

Agents created outside lettabot (via ADE, Letta Cloud) won't have the
system prompt telling them about <no-reply/>. Adding the hint to group
chat envelopes makes the opt-out mechanism self-documenting.

Written by Cameron ◯ Letta Code

"Silence is one of the great arts of conversation." -- Marcus Tullius Cicero

---------

Co-authored-by: Gabriele Sarti <gabriele.sarti996@gmail.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

package-lock.json

@@ -7,6 +7,7 @@
     "": {
       "name": "lettabot",
       "version": "1.0.0",
+      "hasInstallScript": true,
       "license": "Apache-2.0",
       "dependencies": {
         "@clack/prompts": "^0.11.0",