feat: 100 skills milestone — 7 new skills + quality improvements across all 93

New skills added:
- teaching-lesson-plan: structured lesson plans for any subject/audience/setting
- seo-content-brief: complete SEO briefs with intent, competitor gaps, and outline
- media-pitch: story-first journalist pitches with angle development framework
- change-management-plan: stakeholder analysis, comms strategy, adoption metrics
- workshop-facilitation-guide: activity instructions, decision protocols, facilitator moves
- sales-forecasting-model: pipeline model, scenario analysis, assumption log
- tax-planning-checklist: year-end tax planning across income, pension, CGT, reliefs

Quality improvements across all 93 existing skills:
- Standardised description format: "Verb the thing. Use when X. Produces Y."
- Added Required Inputs section to all skills missing it (prompts for missing info)
- Added Quality Checks section to all skills missing it (specific, not generic)
- Fixed broken multiline YAML descriptions
- Removed non-standard frontmatter keys (tool_integration, metadata blocks)

README updated to v6.0.0 with 100-skill count, new skill tables, and article series

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

skills/vendor-evaluation/SKILL.md

@@ -64,6 +64,15 @@ Security: ISO 27001 / SOC 2 certified? Where is data stored? Breach notification
 **Conditions:** [Contract terms to negotiate before signing]
 **Runner-up:** [Vendor and why they lost]
 
+## Quality Checks
+
+- [ ] Evaluation criteria weights total 100%
+- [ ] Scoring rubric is defined before scoring vendors (not post-hoc)
+- [ ] Reference check questions are included
+- [ ] Recommendation includes risks and conditions, not just a winner
+- [ ] Runner-up rationale explains why they lost (enables future conversations)
+- [ ] Contract terms to negotiate are specified
+
 ## Example Trigger Phrases
 - "Help me evaluate vendors for [procurement]"
 - "Create a vendor scorecard for [software/service]"