refactor(api): include type segment in DO names

[braden-w]

DO names currently encode the user but not the resource type—user:{userId}:{resourceName} is the same shape for both workspace and document routes. Since WORKSPACE_ROOM and DOCUMENT_ROOM are separate Cloudflare namespaces, idFromName() produces different DO instances, so this hasn't caused runtime issues. But the name strings themselves are ambiguous: given user:abc:notes, you can't tell if it's a workspace or a document without additional context.

This becomes a real problem for any tracking or observability layer that stores DO names. A UNIQUE constraint on doName would collide when a user has a workspace and document with the same name, and log entries become unparseable without the namespace context that produced them.

The fix adds a type segment to every DO name:

user:{userId}:{type}:{name}

Both stub functions in app.ts change from a bare resource name to an explicit type prefix:

// Before
function getWorkspaceStub(c: Context<Env>) {
    const doName = `user:${c.var.user.id}:${c.req.param('workspace')}`;
    return c.env.WORKSPACE_ROOM.get(c.env.WORKSPACE_ROOM.idFromName(doName));
}

// After
function getWorkspaceStub(c: Context<Env>) {
    const doName = `user:${c.var.user.id}:workspace:${c.req.param('workspace')}`;
    return c.env.WORKSPACE_ROOM.get(c.env.WORKSPACE_ROOM.idFromName(doName));
}

Same pattern for getDocumentStub—:document: instead of bare name.

┌─────────────────────────────────────────────────────────┐
│  Route                              │  DO Name          │
├─────────────────────────────────────┼───────────────────┤
│  GET /workspaces/epicenter.tab-mgr  │  Before: user:abc:epicenter.tab-mgr          │
│                                     │  After:  user:abc:workspace:epicenter.tab-mgr │
├─────────────────────────────────────┼───────────────────┤
│  GET /documents/my-note             │  Before: user:abc:my-note                     │
│                                     │  After:  user:abc:document:my-note             │
└─────────────────────────────────────┴───────────────────┘

Migration

Clean break—same approach as the tab-manager → epicenter.tab-manager rename. Local-first clients hold the full Y.Doc locally and re-sync to the new (empty) DO on next connection. Old DOs sit idle until cleanup. Document snapshots stored in old DO SQLite are lost, which is acceptable during early development.