feat: improve memory prioritization — user preferences over procedural knowledge

Inspired by OpenAI Codex's memory prompt improvements (openai/codex#14493)
which focus memory writes on user preferences and recurring patterns
rather than procedural task details.

Key insight: 'Optimize for reducing future user steering — the most
valuable memory prevents the user from having to repeat themselves.'

Changes:
- MEMORY_GUIDANCE (prompt_builder.py): added prioritization hierarchy
  and the core principle about reducing user steering
- MEMORY_SCHEMA (memory_tool.py): reordered WHEN TO SAVE list to put
  corrections first, added explicit PRIORITY guidance
- Memory nudge (run_agent.py): now asks specifically about preferences,
  corrections, and workflow patterns instead of generic 'anything'
- Memory flush (run_agent.py): now instructs to prioritize user
  preferences and corrections over task-specific details

tools/memory_tool.py

@@ -439,11 +439,13 @@ MEMORY_SCHEMA = {
         "Memory is injected into future turns, so keep it compact and focused on facts "
         "that will still matter later.\n\n"
         "WHEN TO SAVE (do this proactively, don't wait to be asked):\n"
+        "- User corrects you or says 'remember this' / 'don't do that again'\n"
         "- User shares a preference, habit, or personal detail (name, role, timezone, coding style)\n"
         "- You discover something about the environment (OS, installed tools, project structure)\n"
-        "- User corrects you or says 'remember this' / 'don't do that again'\n"
         "- You learn a convention, API quirk, or workflow specific to this user's setup\n"
         "- You identify a stable fact that will be useful again in future sessions\n\n"
+        "PRIORITY: User preferences and corrections > environment facts > procedural knowledge. "
+        "The most valuable memory prevents the user from having to repeat themselves.\n\n"
         "Do NOT save task progress, session outcomes, completed-work logs, or temporary TODO "
         "state to memory; use session_search to recall those from past transcripts.\n"
         "If you've discovered a new way to do something, solved a problem that could be "