feat(framework): MOS-STE writing standard + Google-style code + per-user comms choice

Adds the agent output standard to the framework SOT so it injects at launch and
is selectable per user (closes the gap: it lived only as a jarvis-brain lab doc + issue #960).

- guides/WRITING-STYLE.md: MOS-STE (adapted ASD-STE100) for docs, Google Style for code,
  verification-artifact emphasis, absolute user-voice carve-out. Written in MOS-STE.
- defaults/STANDARDS.md: Output-standards block (always injected via the prompting contract).
- defaults/AGENTS.md: routing row so writing/doc/comms work reaches the guide.
- defaults/USER.md: per-user 'Comms style' option (technical|prose|brief), default technical.

Refs mosaicstack/stack#960. Owner directive (Jason, 2026-07-30): docs->adapted ASD-STE100,
code->Google style, resumes/personal carved out, comms style a per-user choice.

Written-by: jarvis (dragon-lin)
Co-Authored-By: Claude Fable 5 <[email protected]>

packages/mosaic/framework/defaults/USER.md

@@ -26,6 +26,18 @@ It is loaded globally and applies regardless of runtime or project.
 - No sycophancy
 - Executive summaries and tables for overview
 
+### Comms style (agents read this to choose how they talk to you)
+
+Choose one. Agents match it for user-facing messages. The default is `technical`.
+This setting governs comms only. It does not change the documentation standard
+(`guides/WRITING-STYLE.md`), which is always MOS-STE.
+
+- **`technical`** (default) — MOS-STE structure: short, active, defined terms.
+- **`prose`** — full sentences and paragraphs, warmer register, fewer tables.
+- **`brief`** — status lines and bullet points, minimum words.
+
+> Comms style: technical
+
 ## Personal Boundaries
 
 (Add any personal boundaries or preferences agents should respect.)