web: surface workflow slug in UI and URLs

[adityachoudhari26]

Part of #1127. Depends on #1131.

Scope

Replace UUID with slug as the workflow identifier across the web app.

Changes

• Workflow routes: switch path segments from :workflowId (uuid) to :workflowSlug.
• Copy-id / "ID" buttons on workflow pages: show slug, keep an option to copy the UUID where it's still useful (webhooks, internal debugging).
• Any API/curl example snippets in the UI: use the slug.
• Decide bookmark migration: short-lived UUID redirect, or accept the break.