fix(website): point workflow references at @rivet-dev/workflows

[jog1t]

Workflows moved from `rivetkit/workflow` to the standalone `@rivet-dev/workflows` package. This updates the website-owned references.

• `/workflows`: the `invoice.ts` hero example was read from the actors docs root. That copy still used the old `actor({ run: workflow(...) })` API, right next to an `npm install @rivet-dev/workflows` button. The example now comes from the workflows docs root, and the GitHub source and example links point at `rivet-dev/workflows`.
• `/agentos`: the workflows code tab uses `workflow({...})` from `@rivet-dev/workflows`.
• The "Every workflow is an Actor run handler" copy (`/workflows`, `/actors`) and the Workflows FAQ now describe `workflow({...})` as the actor definition. The FAQ's GitHub link points at the new repo.
• In the agent setup prompt, the Workflows `issuesUrl` is now `rivet-dev/workflows/issues`.
• Deleted the unreferenced `src/data/use-cases.ts` and the stale "workflows docs unwritten" row in `HIDDEN.md`.

The vendored actors, agentOS, and Dynamic Apps docs still carry old snippets until they are re-synced from the product repos. The actors fix is rivet-dev/actors#5752.

Checked on a local dev server: `/workflows`, `/actors`, and `/agentos` contain no `rivetkit/workflow` references.

[the-company-company]

🟠 1 medium-severity finding

_{Reviewed commit 09d6ae3.}

[the-company-company]

🟠 Medium · The combined agentOS workflow example does not type-check

@rivet-dev/agentos currently depends on exactly rivetkit@2.3.10, while @rivet-dev/workflows requires the peer range >=2.3.11 <2.4.0. That gives this example two RivetKit copies: workflow() returns the 2.3.11 ActorDefinition, but agentOS's setup() accepts the 2.3.10 class. Because ActorDefinition contains a private #config field, those classes are nominally incompatible, so the later setup({ use: { vm, codeReview } }) fails type checking.

Align the agentOS and Workflows packages on one compatible RivetKit version before publishing this cross-product example, and type-check the complete snippet against those package versions.

[jog1t]

Confirmed, and it's a packaging issue in @rivet-dev/agentos, not in this snippet.

What I checked:

• @rivet-dev/agentos pins rivetkit to exactly 2.3.10 in latest (0.2.19), rc (0.2.20-rc.1), and main (0.0.0-main.5ac5a14). @rivet-dev/workflows@1.0.0 needs rivetkit >=2.3.11 <2.4.0.
• In a clean install of agentos 0.2.19, @agentos-software/pi 0.2.7, and workflows 1.0.0, npm installs two copies (rivetkit 2.3.10 and 2.3.17). Running tsc --noEmit on the server.ts part fails with TS2344: Property '#private' in type 'Registry' refers to a different member on step.client<typeof registry>().
• With an npm override that forces one rivetkit@2.3.17, the same snippet type-checks with no errors. So the code is right once there's only one RivetKit copy.

Why I didn't swap in setup from @rivet-dev/workflows: that variant does type-check, but it skips what agentOS's own setup configures (experimentalActorUds: true, which the VM sidecar uses for SQLite, plus larger message size limits). It would also still load two RivetKit runtimes. It would pass tsc and then break the VM at runtime.

I left the snippet as the intended API. The fix is to widen @rivet-dev/agentos's rivetkit dependency to include >=2.3.11 (or make it a peer dependency), which is being handled separately in rivet-dev/agentos.