Fix uv sync instructions for monorepo workspace

[talkasab]

Problem

After cloning or pulling, uv sync only installs the root project's dependencies in a uv workspace. It silently drops workspace member packages and their deps (e.g., duckdb from oidm-common). The correct command is uv sync --all-packages, but this isn't documented in user-facing places.

What needs fixing

• README.md:102 — change uv sync to uv sync --all-packages
• Add a task install target to Taskfile.yml that runs uv sync --all-packages
• CLAUDE.md — mention task install or uv sync --all-packages in workflow section
• .github/copilot-instructions.md — same

Context

Discovered when pulling dev on a second machine and running task test — all oidm-common tests failed with ModuleNotFoundError: No module named 'duckdb'.