fix(skills): close description-vocabulary gaps, raise rank-1 floor to 95

Eleven positive trigger prompts ranked their skill #2-#3 because the
descriptions lacked vocabulary users actually say (follow-up to #351):

- debugging-and-error-recovery: regression vocabulary (worked yesterday,
  what broke)
- documentation-and-adrs: 'document an architecture decision', design
  reasoning ('documentation' and 'document' don't stem together)
- doubt-driven-development: cross-examining assumptions, stress-testing
  a plan for hidden failure modes, high-stakes changes
- git-workflow-and-versioning: splitting a messy working tree into
  atomic commits
- incremental-implementation: thin/verifiable slices, next task from a
  plan, feature flags
- shipping-and-launch: what needs to be in place before shipping
- spec-driven-development: PRD, objectives and scope
- test-driven-development: red-green-refactor
- using-agent-skills: deciding which workflow applies to the work
- source-driven-development: verify against the official docs
  ('docs'/'documentation' don't stem together)

Trigger rank-1 rate: 86% -> 100% (76/76), no new collision warnings.
CI floor raised from 80 to 95 per the ratchet policy; README baseline
updated and the stale #351 tracking sentence rephrased as guidance.

skills/source-driven-development/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: source-driven-development
-description: Grounds every implementation decision in official documentation. Use when you want authoritative, source-cited code free from outdated patterns. Use when building with any framework or library where correctness matters.
+description: Grounds every implementation decision in official documentation. Use when you want to verify an approach against the official docs before implementing it, or when you want authoritative, source-cited code free from outdated patterns. Use when building with any framework or library where correctness matters.
 ---
 
 # Source-Driven Development