feat: validate and document demo source scenarios (Pokemon, GitHub, CSV, Stripe, Notion)

[db-tycoon-stephen]

Summary

The following demo source scenarios have been designed but not yet tested end-to-end:

Scenario	Source type	Notes
Pokemon API	rest_api (dlt rest_api source)	Best first demo — no auth needed
GitHub	github (dlt github source)	Requires GitHub token; good catalog demo
CSV / local files	filesystem	Good for user-supplied data
Stripe	stripe_analytics (dlt stripe source)	Requires API key
Notion	notion (dlt notion source)	Requires integration token

What's needed

For each scenario:

1. Run tycoon sources add <type> → tycoon sources install <type> → tycoon ingest run <name>
2. Confirm dlt init succeeds and the _run.py shim works
3. Confirm dbt staging models exist or scaffold them with tycoon explore
4. Confirm data appears in Rill once Rill connector (issue Rill: DuckDB connector opens internal temp DB instead of warehouse file #5) is fixed

Start with Pokemon API as it requires no credentials and makes the best first-run demo.

[db-tycoon-stephen]

Closing — the two zero-credential scenarios are verified end-to-end:

• Pokemon API (rest_api): Full flow tested on a fresh directory: tycoon init → sources add rest_api → sources run pokeapi → analyze pokeapi --rill → Rill starts clean with all resources reconciled.
• CSV (filesystem): Verified with single-file path; fixed _read_csv table naming and filesystem shim single-file detection.

GitHub, Stripe, and Notion shims are in place but require real credentials to validate — tracking separately as needed.