Design root-problem extraction conversation flow

**Context**
The conversation design for the AI-coached intake (#20). What questions, in what order, draw out the real problem from nonprofits without overwhelming them?

**Done looks like**
- Conversation script / decision tree
- 3+ test runs with real nonprofit POCs
- Comparison vs. current static form

**Notes**
This is a UX research task as much as a product one.
