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/research-protocol/SKILL.md

@@ -86,10 +86,11 @@ Qualitative: [Framework — e.g. Braun & Clarke], [quality assurance]
 | Write-up | | | |
 
 ## Quality Checks
-- Primary objective is singular and answerable
-- Sample size has stated basis
-- Ethical considerations complete
-- Analysis plan pre-specified
+- [ ] Primary objective is singular and answerable (not compound)
+- [ ] Sample size has a stated basis (power calculation or saturation rationale)
+- [ ] Ethical considerations section is complete
+- [ ] Analysis plan is pre-specified (not "to be determined")
+- [ ] Timeline includes all phases from ethics approval to write-up
 
 ## Example Trigger Phrases
 - "Write a research protocol for [study]"