docs: improve the founder-idea-evaluator sample wiki

[kms970]

Goal

Improve the built-in founder-idea-evaluator example so first-time users can understand what a high-quality Mindpack source wiki looks like.

Suggested scope

• Review the current files under examples/founder-idea-wiki/.
• Add or improve short comments/sections that explain why each folder exists.
• Keep the content generic and public-safe.
• Do not add private founder notes, real company names, or real user data.

Acceptance criteria

• The example remains small and readable.

• The wiki still compiles with:

  python3 -m mindpack_kit compile examples/founder-idea-wiki --out dist/founder-idea-evaluator --pack-id mindpack.founder-idea-evaluator --title "Founder Idea Evaluator"
  python3 -m mindpack_kit validate dist/founder-idea-evaluator

• python3 -m pytest -q still passes.

Why help wanted

Better examples are the fastest way to help new users understand Mindpack without reading the whole codebase.