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/discovery-call-prep/SKILL.md

@@ -91,6 +91,14 @@ This call is NOT successful if we only pitched and got "sounds interesting, send
 ### Suggested Next Step
 "Based on what we discussed, the logical next step would be [specific]. Does [day/time] work?"
 
+## Quality Checks
+
+- [ ] Research summary includes recent news (last 90 days) — not just LinkedIn bio
+- [ ] Call hypothesis is written before the call (not post-rationalised after)
+- [ ] Discovery questions progress from context → pain → business impact → buying process
+- [ ] Success criteria define what "not successful" looks like (not just the ideal outcome)
+- [ ] A specific next step is proposed (not "let's stay in touch")
+
 ## Example Trigger Phrases
 - "Prepare me for a discovery call with [company/contact]"
 - "Build a call brief for my meeting with [name] at [company]"