Make Unity AI Gateway governance demo more developer-friendly

[djliden]

Lands the content of #20. That PR can't be merged as-is and its author is out for a few weeks, so this re-lands the same change as a fresh branch off main. Nothing is rewritten on #20, and author credit is preserved on the commit (author: Jules Damji, commit 5a58d8b).

Why a fresh branch

main received this demo in #19 from the same source commit #20 is based on (4543795), so README.md and ai_gateway_demo.ipynb conflicted add/add while each side was byte-identical to what the other had replaced. There was no content to reconcile — main's copies are the versions #20 edited. This branch's tree is byte-identical to #20's head (e2dcc5b).

What's in it

• README: cut marketing filler, fixed typos, and corrected the broken model-service step numbering (Acts 7/8 were mis-numbered as config steps). Kept the operational gotchas developers actually hit: how a guardrail block looks, the PII post_call trap, denied requests never reaching the inference table, per-provider response shapes.
• Notebook: removed repetitive "solution" phrasing and marketing slop, fixed typos (Jail break, mau, Act 7 :), dropped a duplicated gw_client assignment.
• Dependencies: added pyproject.toml so the README's uv sync step works — the directory had no dependency manifest.

Verification

• git diff main...dl/uaig-governance-readme-deps is exactly these three files (168 insertions, 128 deletions); nothing else on main is touched.
• Notebook: valid JSON, 31 cells, all 12 code cells compile, all 20 local from <module> import <symbol> references resolve.
• uv lock --dry-run: resolves 185 packages against the Databricks PyPI proxy, exit 0, no conflicts.
• Ruff: with the new [tool.ruff] config, this branch and main's content report the identical 18 findings (15× E501, W291, W293, I001) — none added, none removed. No CI runs ruff; flagging it so the config isn't read as a passing gate.

Follow-up

Once this lands, #20 can be closed as superseded.