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/sop-writer/SKILL.md

@@ -81,11 +81,12 @@ NOTE: Steps must be written in imperative form. Each step must have one action o
 | 1.0 | [Date] | [Name] | Initial release |
 
 ## Quality Checks
-- All steps in imperative form
-- Each step has exactly one action
-- Roles specified for every step
-- Quality checkpoints at critical stages
-- Non-conformance process defined
+- [ ] All steps written in imperative form ("Open...", "Navigate...", "Confirm...")
+- [ ] Each step has exactly one action
+- [ ] Role specified for every step
+- [ ] Quality checkpoints at critical stages
+- [ ] Non-conformance process defines who to notify and how to document
+- [ ] Document history table and review date are included
 
 ## Example Trigger Phrases
 - "Write an SOP for [process]"