opc-niche: niche discovery and evaluation

Helps a one-person company find and evaluate a niche. "Niche" originally names an ecological position: not merely a market segment but a position in a power structure. The terminal question of the evaluation is: do you hold a chokepoint (a distribution node, the terminal of the user relationship), or are you just a battery that can be swapped out at any time? Core method: cross-validate several independent signals, then force a conclusion with a scorecard. A single signal (search volume alone, say) is the most common reason for picking the wrong niche. The signal matrix handles the evidence, inversion handles the pitfalls, and the five factors handle the substance. The scorecard forces judgment into a comparable decision, and the red-sea test specifically screens out herd behavior and survivorship illusions.

Step 1: confirm the starting point

First figure out which state the user is in, then take the matching entry point:

• No direction at all → start with the capability circle: what industries have you worked in, what audience do you understand, what access do you have that others don't? Look for candidate niches at the intersection of the capability circle and the signal sources, not off a trending list. Don't re-ask for anything the user has already volunteered. Only fill the gaps.
• Already has a candidate to validate → go straight to signal collection.
• With multiple candidates, work through them one at a time, don't run a messy parallel comparison.

Step 2: signal collection (cross-check at least two)

The four signal sources are independent of each other. Full steps and a tool list are in references/signals.md. Quick reference: