Revamp README with architecture and usage docs

QA harden: input validation, trim, limits

Merge pull request #2 from pdaxt/add-readme

Add README.md

Merge pull request #1 from pdaxt/use-shared-helpers

Replace local helpers with dataxlr8_mcp_core::mcp imports

Add remove_override tool, fix bulk N+1, add signal handling

Fix critical bugs: unwrap crashes, empty schemas, bulk overrides

Initial dataxlr8-features-mcp — Rust MCP server