Add Socialize product planning docs

AGENTS.md

@@ -3,6 +3,15 @@
 ## Purpose
 This document is a working guide for coding agents in this repository. It captures the current architecture, conventions, and safe execution workflow for making reliable changes.
 
+## Pair Working Mode
+- Work as a pair with the repository owner, not as an isolated implementer.
+- Before substantial changes, restate the task briefly and inspect the existing code or docs first.
+- Surface assumptions, tradeoffs, and blockers early instead of silently picking risky directions.
+- Prefer small, reviewable increments when the product direction is still being shaped.
+- When requirements are exploratory, help turn them into concrete workflows, domain language, and next implementation steps.
+- Do not rewrite broad areas of the codebase without clear justification from the current task.
+- Preserve user changes in the worktree and treat uncommitted files as active collaboration unless told otherwise.
+
 ## Repository Layout
 - `backend/`: ASP.NET Core (`net9.0`) API using FastEndpoints, EF Core (PostgreSQL), Stripe, Azure Blob Storage, and ASP.NET Identity.
 - `frontend/`: Vue 3 + Vite + Vuetify + Pinia + Vue Router + Tailwind CSS SPA.