skills: add first methodology companion batch

[weicao]

Summary

Add the first direct doc-to-skill conversion batch for high-frequency addon workflows:

• github-submission-discipline
• paramdef-range-validation
• probe-soft-failure
• runner-portability
• soak-test-classification

Also update skills/README.md to list methodology companion skills and the conversion rule: only turn a doc into a skill when it changes agent behavior during coding, testing, reviewing, debugging, or reporting.

Why

Several docs/addon-*-guide.md files already contain repeatable checklists and decision flows. Keeping them only as prose makes agents less likely to apply them at the moment of work. These five are the first batch because they have clear triggers and concrete failure modes.

Validation

• git diff --check HEAD~1 HEAD
• plugin manifest validation passed with the existing root context warning only
• new-process smoke for all five skills:
  • /github-submission-discipline Say exactly: LOADED
  • /paramdef-range-validation Say exactly: LOADED
  • /probe-soft-failure Say exactly: LOADED
  • /runner-portability Say exactly: LOADED
  • /soak-test-classification Say exactly: LOADED

Notes

github-submission-discipline intentionally contains detector strings for commit and PR body hygiene checks.