Migrate remaining Poetry tooling to uv

[Copilot]

Following the repository-wide switch from Poetry to uv, the contributor-facing tooling still referenced Poetry. This updates the docs, git hooks, dev container, and sample projects, and removes the stale .github/copilot-instructions.md.

Changes

• .github/copilot-instructions.md — removed.
• CONTRIBUTING.md — uv install link and uv sync --group ... commands; dropped the Poetry-specific debugpy/WheelFileValidationError note.
• .githooks/pre-commit / pre-push — availability guard now checks for uv instead of poetry.
• .devcontainer/ — Dockerfile installs only uv (removed the Poetry install + poetry config step), pyenv Python bumped 3.9 → 3.10; devcontainer name and README updated.
• samples/react-agent-docintelligence/ — pyproject.toml converted to the uv_build backend with [dependency-groups]; Makefile switched to uv run; README updated; obsolete poetry.lock removed.
• samples/foundry-memory/README.md — wording updated to reference the uv environment.

Notes

The sample's [tool.poetry] table maps to the uv build backend, preserving the src/react_agent layout via an explicit module-name:

[build-system]
requires = ["uv_build>=0.8,<0.12"]
build-backend = "uv_build"

[tool.uv.build-backend]
module-root = "src"
module-name = "react_agent"

[dependency-groups]
dev = ["mypy>=2.1.0", "ruff>=0.15.20", "pytest>=9.1.1", "pytest-asyncio", "vcrpy"]

A uv.lock for the react-agent sample is not included: lock resolution hits a pre-existing upstream constraint conflict (langchain-azure-ai ↔ azure-ai-contentunderstanding prerelease) unrelated to this migration. uv build succeeds and packages react_agent correctly.