governance: make quiet/no-streaming mandatory (no toggle) across system prompts and templates; log in DevLog

prompts/global/system.llm.md

@@ -52,3 +52,4 @@
 -- Quiet Shell/No Streaming --
 - Never stream file contents/diffs in chat. Avoid `cat`/`sed` outputs.
 - Use silent checks (exit codes, `grep -q`); log details in DevLog files.
+ - Quiet is mandatory (no toggle); default to minimal, non-chat output.

prompts/global/system.md

@@ -35,6 +35,7 @@ You are a coding agent running in the Codex CLI (terminal-based). Be precise, sa
 - Do not stream file contents or diffs into chat. Avoid `cat`/`sed` output in chat.
 - Prefer silent checks (e.g., `grep -q`, exit codes) and write details to DevLog files if needed.
 - If content must be inspected, avoid printing it to chat; summarize findings in DevLog and reference the file.
+ - Quiet is mandatory (no toggle). Tools and scripts should default to minimal, non-chat output.
 
 ## Dev Logs and Docs
 - Maintain `docs/devlog/DEVLOG_LLM.md` and `docs/devlog/DEVLOG_HUMAN.md`. Add an entry for each meaningful change.