Add directory-submissions skill

New skill covering directory-driven distribution: startup/SaaS/AI/agent/MCP/no-code
directories, Product Hunt prep, Reviews playbook (G2/Capterra 10-in-30 protocol),
GEO optimization, destination pages strategy, and Reddit/LinkedIn community loops.

Includes:
- SKILL.md (376 lines) with workflow, PH 3-week timeline, reviews protocol, KPIs
- references/directory-list.md — full tiered catalog with DR, dofollow, notes
- references/positioning-variations.md — per-tier copy templates (7 tiers)
- references/submission-tracker-template.csv — ready-to-use tracker with 78 rows

Registered in marketplace.json and README skill table (alphabetical).

.claude-plugin/marketplace.json

@@ -28,6 +28,7 @@
         "./skills/copy-editing",
         "./skills/copywriting",
         "./skills/customer-research",
+        "./skills/directory-submissions",
         "./skills/email-sequence",
         "./skills/form-cro",
         "./skills/free-tool-strategy",