[codex] Merge package into teich and fix CI workflow

[owenqwenstarsky]

What changed

• merged the implementation package into teich and removed the old agentic_datagen namespace
• extracted shared prompt, schema, and trace helpers into src/teich/utils
• updated the GitHub Actions workflow to run from the repo root instead of the removed v2/ path
• refreshed the workflow Docker image tag to match the current project

Why

The codebase had split package ownership between teich and agentic_datagen, plus duplicated helper logic. Separately, CI was failing because the workflow still assumed the project lived under v2/, so the jobs exited before running tests or Docker builds.

Impact

• teich is now the single source of truth for the package implementation
• shared parsing and schema logic is centralized for easier maintenance
• GitHub Actions should run against the current repo layout again

Validation

• uv run --extra dev pytest tests/test_cli.py tests/test_config.py tests/test_converter.py tests/test_formatter.py tests/test_loader.py tests/test_trace_readme.py tests/test_runner.py -q
• uv run --extra dev pytest tests/test_integration.py -q
• uv run --extra dev ruff check src tests

Notes

• left uv.lock uncommitted because its diff was local tool churn rather than part of the package/CI fix

[armand0e]

Thanks. will look into what's remaining.