v0.4.0 ArcadeDB embedded mode added, pypi built releases (0.4.0)

ArcadeDB embedded mode added, pypi built releases (0.4.0) for flexible-graphrag and flexible-graphrag-mcp, readme updated, search fixes

1. ArcadeDB embedded mode: factories.py, config.py, env-sample.txt — runs in-process via ARCADEDB_MODE=embedded; optional HTTP/Studio via ARCADEDB_EMBEDDED_SERVER=true; arcadedb-embedded>=26.2.1 added as commented-out dependency
2. llama-index-graph-stores-arcadedb bumped to >=0.4.1 in requirements.txt and pyproject.toml for embedded seport
3. hybrid_system.py: X->REL->Y bare relation links filtered in all modes (not just graph-only); filtered before top_k slice
4. hybrid_system.py: Elasticsearch/OpenSearch-only ingestion error fixed
5. pyproject.toml: version 0.4.0; PEP 639 license; all 14 py-modules; incremental_updates package; Dockerfile/env-sample/requirements/uv.toml in sdist; placeholder README.md
6. start.py + pyproject.toml: flexible-graphrag console script entry point added
7. flexible-graphrag-mcp/pyproject.toml: version 0.4.0; Apache 2.0 license; author; readme reference
8. .gitignore: arcadedb_data/ and log/ excluded
9. README.md: badges added, backend pip install from pypi quickstart added; MCP server quickstart setup section added, mcp tools moved after; project/file structure updated; UI Usage moved after frontend setup; Testing cleanup mentions cleanup.py