fix(template): address temp todo review (copier, tooling, sync parity)

[buddingengineers12345]

Summary

This PR applies the remaining actionable items from the internal temp_todo.md review (delta vs the current tree): Copier post-generation behavior, stricter package_name validation, explicit coverage targets, safer install and pre-commit hook invocations, gitignore and Ruff documentation cleanup, and root/template parity.

Changes introduced

• copier.yml: Use uv sync (without --frozen) immediately after uv lock in _tasks; tighten package_name with isidentifier(); document github_actions_python_versions JSON string for fromJson() in workflows.
• justfile (root + template): Add --cov=scripts / --cov={{ package_name }} for coverage and CI test recipes; replace install with Astral bootstrap when uv is missing.
• Pre-commit: Use uv run --active for local Ruff and BasedPyright hooks; mirror to template/.pre-commit-config.yaml.
• GitHub Actions: tests.yml and generated ci.yml.jinja use explicit --cov= targets aligned with justfiles.
• .gitignore (root + template): Remove TESTING_STREAMLIT.md exception and stray /1.
• pyproject (root + template): Document why E501 is ignored under Ruff lint.
• Tests: New integration test for invalid package_name; update test_ci_workflow_aligns_with_just_ci for explicit coverage flags.

Testing

• just sync-check
• just ci (full pipeline)
• Targeted pytest: test_ci_workflow_aligns_with_just_ci, test_package_name_validator_rejects_non_identifier

Documentation

• Not applicable (inline comments and template comments only; no user-facing docs folder changes).

Related issues

• N/A (internal checklist)

Contributor checklist

Please confirm the following before submitting:

• I have read and followed the Contributing Guidelines
• Tests have been added or updated as appropriate
• Documentation has been updated where necessary
• Linting and formatting pass locally
• CI checks are passing

Release notes

If this change affects users, please indicate whether a release note is required:

• A release note has been added
• This change does not require a release note

Additional notes

Generated projects: post-gen uv sync no longer uses --frozen immediately after uv lock, matching the lockfile produced in the same task run.

Thank you for your contribution.