fix(release): unbreak simple_module_cli build + guard at PR time

[antosubash]

Summary

• The last release run (25247762589) failed building simple_module_cli with FileNotFoundError: Forced include not found: .../sdists-v9/skills. Root cause: framework/cli/pyproject.toml had [tool.hatch.build.targets.wheel.force-include] pointing at ../../skills, which works for a direct source build but breaks the standard PEP 517 sdist→wheel rebuild that uv build --all-packages performs (the unpacked sdist has no parent skills/).
• simple_module_cli/skills is already a symlink to the repo-root skills/, and hatchling follows symlinks during both sdist and wheel builds, so the exclude + force-include pair was both unnecessary and actively broken. Dropping it is the fix.
• PR checks didn't catch this because pr.yml had no packaging job — uv build only ran on the manually-dispatched release workflow. Adding a package-build job that mirrors release.yml closes that gap.

Changes

• framework/cli/pyproject.toml — drop exclude + force-include, rely on hatchling's symlink-following.
• framework/cli/tests/test_build_packaging.py — new pytest module that runs uv build --package simple_module_cli and asserts the wheel + sdist ship simple_module_cli/skills/* and simple_module_cli/templates/*. Confirmed it fails on the old config and passes on the fix.
• Makefile — new ci-build-packages target running uv build --all-packages, the same invocation release.yml uses.
• .github/workflows/pr.yml — new package-build job calling make ci-build-packages, added to the pr-checks aggregate so it's required by branch protection.

Test plan

• uv build --all-packages builds all 13 packages cleanly locally
• uv run pytest framework/cli/tests/ — 97/97 passing
• Regression test verified: it fails on the broken config and passes on the fix
• make ci-build-packages succeeds locally
• CI's new package-build job goes green on this PR
• After merge, re-run the release workflow and confirm it ships