fix(pyproject.toml): resolve duplicate dependency tables via PEP 621

[Abhijith-2002]

Fix pyproject.toml duplicate dependency tables by aligning with PEP 621

Problem:

The current pyproject.toml declares dependencies twice under
[tool.poetry] and [tool.poetry.dependencies], which creates duplicate table declarations and is invalid TOML.

This causes:

• poetry install to fail with a duplicate table error
• uv sync to fail during TOML parsing

Solution:

• Move project metadata and dependencies to [project] per PEP 621
• Retain [tool.poetry.dependencies] for Poetry compatibility
• Remove duplicate dependency declaration

Verification:

Before:

abhijith@Abhijiths-MacBook-Air RAG % poetry install

/Users/abhijith/adk-samples/python/agents/RAG/pyproject.toml is not a valid TOML file.
TOMLDecodeError: Cannot declare ('tool', 'poetry', 'dependencies') twice (at line 21, column 26)

abhijith@Abhijiths-MacBook-Air RAG % uv sync
warning: Failed to parse `pyproject.toml` during settings discovery:
  TOML parse error at line 21, column 14
     |
  21 | [tool.poetry.dependencies]
     |              ^^^^^^^^^^^^
  duplicate key

error: Failed to parse: `pyproject.toml`
  Caused by: TOML parse error at line 21, column 14
   |
21 | [tool.poetry.dependencies]
   |              ^^^^^^^^^^^^
duplicate key

After:

abhijith@Abhijiths-MacBook-Air RAG % poetry install
Creating virtualenv rag-ZkpOJD3b-py3.11 in /Users/abhijith/Library/Caches/pypoetry/virtualenvs
Updating dependencies
Resolving dependencies... (79.4s)

Package operations: 170 installs, 0 updates, 0 removals

abhijith@Abhijiths-MacBook-Air RAG % uv sync
Resolved 197 packages in 1.57s
      Built rag @ file:///Users/abhijith/adk-samples/python/agents/RAG