fix: use console.error for debug messages to prevent MCP JSON parse errors

[amihos]

Summary

• MCP protocol requires stdout to contain only valid JSON-RPC messages
• Debug messages like [DB] Using... written to stdout cause Claude Desktop to fail with "Unexpected token" JSON parse errors
• Changed all console.log statements with debug prefixes to console.error so they go to stderr instead

Problem

When starting Claude Desktop with OpenMemory MCP server, users get errors like:

MCP openmemory: Unexpected token 'D',"[DB] Using ... is not valid JSON

This happens because the MCP server outputs debug messages to stdout, which Claude Desktop tries to parse as JSON-RPC responses.

Solution

Changed all tagged console.log calls (e.g., [DB], [MCP], [CONFIG], [MIGRATE], etc.) to console.error so they go to stderr instead of polluting the stdout JSON stream.

Files Changed

• backend/src/ai/mcp.ts
• backend/src/core/db.ts
• backend/src/core/migrate.ts
• backend/src/core/models.ts
• backend/src/core/telemetry.ts
• backend/src/memory/decay.ts
• backend/src/memory/embed.ts
• backend/src/memory/reflect.ts
• backend/src/migrate.ts
• backend/src/ops/dynamics.ts
• backend/src/ops/ingest.ts
• backend/src/server/index.ts
• backend/src/server/middleware/auth.ts
• backend/src/temporal_graph/store.ts

Test Plan

• Start Claude Desktop with OpenMemory MCP configured
• Verify no JSON parse errors on startup
• Verify MCP tools work correctly (query, store, list, etc.)
• Check that debug logs still appear in stderr/container logs

🤖 Generated with Claude Code

[nullure]

Please test the code on your system

[amihos]

Closing this PR as it has developed merge conflicts due to upstream changes since it was created.

The fix is still relevant - there are still ~10 console.log("[...") statements that can pollute stdout during MCP stdio mode. Will create a fresh PR with the same fix applied cleanly to current main.

See replacement PR to follow.