fix: align optional-extras pins so uv sync resolves - #2794

Why are these changes needed?

uv sync fails on a fresh clone because several optional extras in pyproject.toml carry pins that conflict with each other or with their own transitive dependencies. pip install resolves greedily for the active interpreter and silently picks one path, so the conflicts stay invisible to it; uv cross-resolves the full extras matrix and surfaces them. Issue #2770 enumerates the specific cases.

pyproject.toml only:

• [rag]: widen llama-index-llms-openai and llama-index-embeddings-openai upper bounds to <0.8. llama-index>=0.14.13 transitively requires the newer sub-package versions, so the previous <0.6 pins made [rag] internally inconsistent.
• [neo4j]: align llama-index / llama-index-core to >=0.14.13,<0.15 (matching [rag]) so the two extras can co-install. Bump llama-index-graph-stores-neo4j and llama-index-readers-web upper bounds to <0.7 accordingly.
• [autobuild]: align chromadb to >=1.4.1,<1.5 (matching [retrievechat]).
• [test]: replace exact pins with ranges. fastapi>=0.115.0,<1 (was ==0.116.1, blocked [nlip] whose nlip-server requires fastapi<0.116.0) and pandas>=2.2.0,<3 (was ==2.3.3, conflicted with llama-index-readers-file<0.5.6).

Validated locally: uv lock --no-cache resolves successfully on Python 3.13 with uv 0.11.7 (802 packages); without these changes resolution fails with the conflicts listed in #2770.

The graphrag_sdk==0.8.2 / pypdf / pandas chain (issue conflict #5) is not pinned here; it resolves transitively through llama-index-readers-file. Adding uv sync to CI (issue suggestion #5) is intentionally out of scope.

Related issue number

Fixes #2770

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