docs: dedupe walkthrough posts a record the server rejects #575

What

The dedupe walkthrough in docs/src/content/docs/development.md:243-252 posts a record the server rejects, and annotates it with a response the server never sends.

The page creates clicks itself at development.md:69-75 as page / button / score / received_timestamp. The walkthrough then posts:

{"event_id": "550e8400-...", "page": "/home"}

annotated # → {"ok":true} and then # → {"duplicate":true}.

Three things are wrong with that:

• internal/discovery/validation.go:24 rejects any key not in the schema, so event_id alone makes this 400 {"error":"unknown column \"event_id\" for table \"clicks\""}. There is no carve-out for the dedupe id field: processRecord runs Validate first (internal/api/ingest.go:526) and only reads data[idField] afterwards (ingest.go:633).
• button and score are non-nullable with no default (score Float64, button String), so they are required too — validation.go:41.
• Consequently neither annotated response can occur.

Fix

Add event_id String to the DDL at development.md:69 and send a complete record in both calls:

{"event_id": "550e8400-...", "page": "/home", "button": "signup", "score": 42.5}

Why it is filed rather than fixed in #555

Found by a docs reviewer during #555, but it is pre-existing — not in that branch's delta — and unrelated to its subject (excluding computed columns from the INSERT column list). Changing the shared clicks DDL on that page has a wider blast radius than the PR warrants, since other examples on the page read against it. Worth doing as its own change so the DDL edit can be checked against every example that depends on it.

Related: the same class of error was just corrected in docs/src/content/docs/sdk/queries.md (insert examples that omitted required button/score) and in several api.md examples, so a sweep for "documented example vs the schema the same page pins" may turn up more.