Documentation: agent-skills coverage gaps

Umbrella / parent issue for documentation gaps that block the [`@harperfast/skills`](https://github.com/HarperFast/skills) rules from migrating to docs-driven generation. Repo-scoped workstream tracked here in `documentation`.

**Why these matter:** each of these rules currently has to stay hand-authored (`mode: synthesized`) because its canonical docs source is missing or thin. Writing the docs here lets the corresponding skill rule be generated from canonical content and stay in sync:

- #538 (table → automatic REST endpoint mapping) → unblocks the `adding-tables-with-schemas` rule
- #539 (UI-independent Fabric account/cluster reference) → unblocks `creating-a-fabric-account-and-cluster`
- #540 (`@harperfast/vite` reference page) → unblocks the Vite half of `serving-web-content` (and relates to `creating-harper-apps`)

Sub-issues attached below.

Start with the attached sub-issues #538, #539, and #540, since this issue is an umbrella for their documentation gaps. Read each sub-issue to identify the missing canonical content for the table-to-REST mapping, Fabric account and cluster reference, and @harperfast/vite reference; done means those docs unblock the corresponding generated skill rules.

Written by the indexing model from the issue text.