fix(skills): add Anti-Patterns and fix descriptions for remaining skills (batch 2)

Processed 24 skills: pr-description-writer through tax-planning-checklist.
Added Anti-Patterns sections to all 24 skills.
Added Required Inputs section to product-launch-checklist.
Rewrote descriptions for retro-analysis, substack-notes-scraper, and sycophancy-challenger.

https://claude.ai/code/session_01MuGKn3a3Gbqoe8uM5Lmuqt

skills/proposal-writer/SKILL.md

@@ -94,6 +94,14 @@ Writes commercial proposals that win business — structured around the prospect
 - [ ] Next steps include a specific date and named action
 - [ ] "Valid until" date is included to create urgency
 
+## Anti-Patterns
+
+- [ ] Do not lead with the solution before establishing that the problem is understood — the proposal must demonstrate problem comprehension first
+- [ ] Do not use vague investment language like "competitive pricing" — every proposal must state a specific price or range
+- [ ] Do not omit a "not included" section — undefined scope leads to disputes after the proposal is accepted
+- [ ] Do not forget a "valid until" date — proposals without expiry create awkward situations and stale pricing
+- [ ] Do not list next steps without naming who is responsible for each and what the expected timeline is
+
 ## Example Trigger Phrases
 - "Write a proposal for [prospect] to [solve their problem]"
 - "Draft a statement of work for [project]"