docs: Replace Mindbase References with ReflexionMemory (#464)

* docs: fix mindbase syntax and document as optional MCP enhancement

Fix incorrect method call syntax and clarify mindbase as optional
enhancement that coexists with built-in ReflexionMemory.

Changes:
- Fix syntax: mindbase.search_conversations() → natural language
  instructions that allow Claude to autonomously select tools
- Clarify mindbase requires airis-mcp-gateway "recommended" profile
- Document ReflexionMemory as built-in fallback (always available)
- Show coexistence model: both systems work together

Architecture:
- ReflexionMemory (built-in): Keyword-based search, local JSONL
- Mindbase (optional MCP): Semantic search, PostgreSQL + pgvector
- Claude autonomously selects best available tool when needed

This approach allows users to enhance error learning with mindbase
when installed, while maintaining full functionality with
ReflexionMemory alone.

Related: #452

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

* docs: add comprehensive ReflexionMemory user documentation

Add user-facing documentation for the ReflexionMemory error learning
system to address documentation gap identified during mindbase cleanup.

New Documentation:
- docs/user-guide/memory-system.md (283 lines)
  * Complete user guide for ReflexionMemory
  * How it works, storage format, usage examples
  * Performance benefits and troubleshooting
  * Manual inspection and management commands

- docs/memory/reflexion.jsonl.example (15 entries)
  * 15 realistic example reflexion entries
  * Covers common scenarios: auth, DB, CORS, uploads, etc.
  * Reference for understanding the data format

- docs/memory/README.md (277 lines)
  * Overview of memory directory structure
  * Explanation of all files (reflexion, metrics, patterns)
  * File management, backup, and git guidelines
  * Quick command reference

Context:
Previous mindbase cleanup removed references to non-existent external
MCP server, but didn't add sufficient user-facing documentation for
the actual ReflexionMemory implementation.

Related: #452

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

* docs: translate Japanese text to English in documentation

Address PR feedback to remove Japanese text from English documentation files.

Changes:
- docs/mcp/mcp-integration-policy.md: Translate headers and descriptions
- docs/reference/pm-agent-autonomous-reflection.md: Translate error messages
- docs/research/reflexion-integration-2025.md: Translate error messages
- docs/memory/pm_context.md: Translate example keywords

All Japanese text in English documentation files has been translated to English.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

---------

Co-authored-by: Claude <noreply@anthropic.com>

README.md

@@ -126,14 +126,17 @@ claude
 For **2-3x faster** execution and **30-50% fewer tokens**, optionally install MCP servers:
 
 ```bash
-# Recommended MCP servers (via airis-mcp-gateway):
-# - Mindbase: Cross-session memory (automatic)
-# - Serena: Session persistence (2-3x faster)
+# Optional MCP servers for enhanced performance (via airis-mcp-gateway):
+# - Serena: Code understanding (2-3x faster)
 # - Sequential: Token-efficient reasoning (30-50% fewer tokens)
 # - Tavily: Web search for Deep Research
 # - Context7: Official documentation lookup
+# - Mindbase: Semantic search across all conversations (optional enhancement)
 
-# Install via: https://github.com/airis-mcp-gateway
+# Note: Error learning available via built-in ReflexionMemory (no installation required)
+# Mindbase provides semantic search enhancement (requires "recommended" profile)
+# Install MCP servers: https://github.com/agiletec-inc/airis-mcp-gateway
+# See docs/mcp/mcp-integration-policy.md for details
 ```
 
 **Performance Comparison:**