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/sprint-brief/SKILL.md

@@ -1,19 +1,20 @@
 ---
 name: sprint-brief
-description: Generate a structured sprint brief from Jira sprint data and goals
-tool_integration: Jira, Slack
+description: "Generate a structured sprint brief from sprint data and goals. Use when asked to write a sprint brief, create a sprint summary, document sprint goals and scope, or produce a team-facing sprint overview. Produces a scannable brief with sprint goal, rationale, grouped work, critical path, risks, and definition of done."
 ---
+
 # Sprint Brief Skill
 
-## Purpose
 Produce a clear, scannable sprint brief that every team member — engineer, designer, PM — can read in under three minutes and understand exactly what we're doing and why.
 
 ## Required Inputs
-- Sprint name and number
-- Sprint goal (1-2 sentences)
-- Ticket list with owners
-- Known dependencies or blockers
-- Carry-over items from previous sprint
+
+Ask the user for these if not provided:
+- **Sprint name and number**
+- **Sprint goal** (1-2 sentences — flag if too vague)
+- **Ticket list with owners** (or a description of the work)
+- **Known dependencies or blockers**
+- **Carry-over items from previous sprint** (if any)
 
 ## Process
 1. Read sprint goal and check it's specific and measurable — flag if it's too vague
@@ -21,11 +22,12 @@ Produce a clear, scannable sprint brief that every team member — engineer, des
 3. Identify the critical path — which tickets must complete for the sprint goal to be met?
 4. Flag risks: tickets with unclear acceptance criteria, missing designs, unresolved dependencies
 5. Note carry-over items and whether they affect this sprint's goal
+6. **Validate** — Confirm the sprint goal is achievable given the ticket scope and capacity. If the critical path items alone would fill the sprint, flag it as overloaded.
 
-## Output Format
+## Output Structure
 
 ### Sprint [Number] Brief — [Dates]
-**Sprint Goal:** [1-2 sentences]
+**Sprint Goal:** [1-2 sentences — specific and measurable]
 **Why This Sprint Matters:** [Connect to quarterly OKR in 2-3 sentences]
 
 **What We're Building:**
@@ -41,3 +43,11 @@ Produce a clear, scannable sprint brief that every team member — engineer, des
 **Carry-over from Last Sprint:** [List + impact on current goal]
 
 **Definition of Done:** [Specific, agreed criteria for sprint success]
+
+## Quality Checks
+
+- [ ] Sprint goal is specific enough to score pass/fail at the end of the sprint
+- [ ] Critical path items are named — not just "the important ones"
+- [ ] Every risk has a mitigation or owner (not just "this is a risk")
+- [ ] Carry-over items are connected to their impact on this sprint's goal
+- [ ] Definition of Done is agreed criteria, not a task list