CI: skip build/test workflows on docs-only pull requests

[mohanchen]

Add paths-ignore to the pull_request triggers of the six heavy build and test workflows (CMake builds, Makefile build, integration/unit tests, CUDA build+test, PyTest, ASE plugin test). Pull requests that only touch docs/**, Markdown files, or .coderabbit.yaml no longer spend runner time on compilation and physics tests that cannot be affected by such changes. Motivated by docs-only PRs such as #8148, which triggered 14 full build/test runs.

Scope notes:

• push triggers (including the develop safety-net runs) are unchanged.
• agent_governance.yml is deliberately untouched: AGENTS.md changes are its primary input and must keep running.
• Workflow file changes themselves are not ignored, so CI changes still trigger CI.

Reminder

• I have read AGENTS.md and docs/developers_guide/agent_governance.md.
• I have linked an issue or explained why this PR does not need one.
• I have added adequate unit tests and/or case tests, or explained why not.
• I have listed the exact verification commands run and their results.
• I have described user-visible behavior changes, including INPUT parameter changes.
• I have explained core-module impact for ESolver, HSolver, ElecState, Hamilt, Operator, Psi, or other source/ changes.
• I have requested any needed governance exception below.

Linked Issue

Fix #

Unit Tests and/or Case Tests for my changes

• Commands run:
• Result summary:
• Checks not run, with reason:

What's changed?

• Example: brief summary of the user-visible or developer-facing change.

Governance Notes

• INPUT/docs changes:
• Core module impact:
• Exceptions requested: