Fix Data Connect skill: upsert key, fetch policy, and emulator workflow

[crrapi]

What

An accuracy pass on the firebase-data-connect-basics skill. Each change fixes something an agent following the current docs hits in practice.

Changes

• examples.md — the Movie Review schema doesn't compile. Review uses a surrogate id PK with @unique(["movie","user"]), but review_upsert keys on the primary key, so it fails with key id is required in upsert but is not set in data. Switched to a composite @table(key: ["movie","user"]) PK (which is also the one-review-per-user guarantee) and updated the dependent MyReviews / DeleteReview operations.
• operations.md — note that _upsert matches on the primary key, not on @unique constraints.
• sdk_web.md — document that queries default to PREFER_CACHE and that fresh/polled/live reads need SERVER_ONLY; correct the fetch-policy call shape to the { fetchPolicy } options object.
• config.md — offline validation / SDK generation runs through the emulator with a demo- project (compile and sdk:generate need credentials); flag that the emulator returns UUIDs without hyphens; clarify outputDir is relative to connector.yaml.
• data_seeding.md — show how to actually execute seeds against the emulator via the generated SDK (the docs never showed a runner).

Notes

Verified against firebase-tools 15.22.3 / dataconnect-emulator 3.4.14 by building a working movie-review app. scripts/format.sh --check passes; docs-only, no skill behavior contract changed.

[gemini-code-assist]

Code Review

This pull request updates the Firebase Data Connect documentation to clarify schema design for upserts (using composite primary keys instead of surrogate IDs), local seeding via the SDK, offline emulator usage, and fetch policy options for the Web SDK. The review feedback correctly points out that generated action shortcuts do not accept fetch policy options directly and suggests updating configuration examples to use the correct relative path depth (../../) to match the new documentation.

[gemini-code-assist]

The generated action shortcuts (such as listMovies) do not accept an options object (like { fetchPolicy }) as an argument. They only accept a DataConnect instance and/or variables. To customize the fetch policy or other execution options, you must use executeQuery with the query reference.

We should remove the incorrect listMovies example to prevent compilation errors for users following this guide.

Suggested change

	await executeQuery(queryRef, { fetchPolicy: QueryFetchPolicy.CACHE_ONLY });
	await executeQuery(queryRef, { fetchPolicy: QueryFetchPolicy.SERVER_ONLY });
	await listMovies(dataConnect, { fetchPolicy: QueryFetchPolicy.SERVER_ONLY });
	await executeQuery(queryRef, { fetchPolicy: QueryFetchPolicy.CACHE_ONLY });
	await executeQuery(queryRef, { fetchPolicy: QueryFetchPolicy.SERVER_ONLY });

[crrapi]

Kept intentionally. The generated query shortcuts do accept ExecuteQueryOptions as the trailing argument — the SDK emits overloads listMovies(dc, options?) and recentReviews(dc, vars?, options?), and passing { fetchPolicy: SERVER_ONLY } to them is verified working on firebase 12.x (it's exactly what turns a stale cached read into a fresh one). Only mutation shortcuts (e.g. addReview) omit the options argument.

[gemini-code-assist]

Since outputDir is resolved relative to the connector.yaml directory (typically dataconnect/connector/), targeting sibling directories at the project root requires walking up two levels (../../). To align with the helpful note added below, we should update the examples in this configuration block (including javascriptSdk and kotlinSdk above) to use ../../ instead of ../ to avoid confusing readers.

Suggested change

	outputDir: "../ios/MyApp/DataConnect"
	outputDir: "../../ios/MyApp/DataConnect"

[crrapi]

Applied in 55a8cf2 — updated the javascriptSdk/kotlinSdk/swiftSdk examples in this block to ../../ so they match the note.