ALL-277: Add Redis MCP server with read-only credentials

Build tools/mcp-servers/redis-mcp/ following the kafka-mcp template. Read-only Redis MCP server (GET, SCAN, KEYS-limited, TYPE, TTL, MEMORY USAGE, DBSIZE, INFO; no SET/DEL/FLUSH). Wire into .mcp.json as texture-redis-prod and texture-redis-local. Deliver PR with .env.prod.example (endpoint host + redacted password). Branch: havoc/all-277-redis-mcp.