Added new customer expansion skill, updated supporting documentation

[andrewrice]

Summary

• Adds customer-expansion skill — frameworks for growing revenue inside existing enterprise accounts (expansion triggers, multi-threading, NRR math, renewal timing)
• Closes the gap in the enterprise playbook: enterprise-account-planning gets to signed, enterprise-onboarding gets through the first 90 days, and now customer-expansion covers what happens
  after — compounding NRR and turning pilots into platform deals
• Updates skill count from 11 → 12 in README.md and AGENTS.md

Why this skill

The existing enterprise skills stop at onboarding. There was no playbook for the 12 months after the contract is signed — when most enterprise revenue is actually lost. Teams default to "we'll expand
at renewal," which is the worst time to sell expansion because procurement is involved and the customer is evaluating alternatives by definition.

This skill gives operators trigger-based expansion timing, a conversation sequence that starts with evidence instead of an ask, NRR leading indicators that surface problems 6 months before the
revenue line does, and multi-threading protocols that prevent single-point-of-failure churn.

Blast radius

Minimal. Three files changed:

• Added: skills/customer-expansion/SKILL.md (new skill, self-contained)
• Modified: AGENTS.md — one line added under Enterprise execution
• Modified: README.md — one table row added, skill count updated 11 → 12

No changes to existing skill content, structure, or dependencies.

How it complements existing skills

Skill	Stage	Handoff point
enterprise-account-planning	Pre-sale → signed deal	Contract signed
enterprise-onboarding	Day 0 → Day 90	First success metric hit
customer-expansion	Day 90 → renewal and beyond	Ongoing — expansion triggers loop back into account planning for new business units

The three skills form a complete enterprise lifecycle. The expansion skill also references enterprise-onboarding directly in its decision trees — if an account hasn't hit its original success
metric, the tree sends the operator back to the onboarding skill before opening any expansion conversation.

Test plan

• skills/customer-expansion/SKILL.md exists and is valid markdown
• AGENTS.md lists customer-expansion under Enterprise execution
• README.md enterprise table includes customer-expansion
• Skill count reads 12 everywhere it previously read 11
• No other files modified

[andrewrice]

@beingsmit The skill is opinionated, feel free to adjust to reflect your own POV. "Under 120%" seems like a reasonable benchmark to me, but I guess it could be stage dependent. I imagine seed-stage companies would be thrilled at 105%. Then series B+ is where 120% starts feeling like a floor. Worth a sanity check against what the other skills assume about stage.