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/account-plan/SKILL.md

@@ -88,7 +88,10 @@ At end of [period]:
 - [Expansion opportunity] progressed to [stage]
 - Health score moved from [current] to [target]
 
-## Example Trigger Phrases
-- "Build an account plan for [customer]"
-- "Create a key account strategy for [account]"
-- "Help me plan my approach to renewing [account]"
+## Quality Checks
+
+- [ ] Relationship map identifies decision-makers, influencers, and any relationship gaps
+- [ ] Risks all have mitigation actions and named owners
+- [ ] Growth opportunities include estimated value (even roughly)
+- [ ] 90-day actions are specific (not "have a call" — what call, with whom, to achieve what)
+- [ ] Success criteria are measurable at the end of the planning period