add llm-banking sample (dozer#1690)

[plurzs01]

working sample for the bank credit-card chatbot use case.

path: usecases/llm-banking/

• Dozer config: LocalStorage CSVs + SQL unified customer_profile + Dummy/ClickHouse sinks
• app: Chroma/local vector retrieval + ranking (offline without a Dozer binary)
• demo: demo.mp4 / scripts/demo.sh
• tests: python -m unittest discover -s tests -v

same sample also lives on getdozer/dozer#2511 (examples/llm-banking/). putting it here since snork-alt said PRs for this bounty belong in dozer-samples.

/claim #1690

[plurzs01]

ready for review when you have bandwidth. sample lives under usecases/llm-banking/, offline CSV path + tests, /claim #1690 in the body. distinct from the chatbot-named PRs if that helps triage.

[plurzs01]

gentle bump — still ready on our side whenever you get a chance. tests under usecases/llm-banking/ pass offline.

[plurzs01]

small follow-up: indexed usecases/llm-banking in the top-level README usecases table so it's easier to spot alongside the other samples.

[plurzs01]

re-ran the offline path today (2026-09-15): 9 tests OK, cust_002 → Travel Signature, cust_003 → Starter Secure. dropped SAMPLE_NOTES.md + refreshed demo-output.txt so the verification steps are easy to skim.