fix(builder): point first-time creators at Content when a picker is empty

Found in real use: with no gatherables authored yet, the Build form's Resource
field has no ⌄ picker (there's nothing to cycle) and nothing explains where
entries come from — so the very first no-code run dead-ends at the moment the
flow should feel best.

A field that references authored content now shows "No Gatherables yet —
create one →" when that category is empty, which jumps straight to the right
Content page. Not a mutation, so it isn't wrapped in a ChangeHistory recording.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

plugin/BuildAdminUi.luau

@@ -220,6 +220,27 @@ function BuildAdminUi.mount(container: Frame, BuildAdmin: any, ContentAdmin: any
 				})
 				row.LayoutOrder = i
 				row.Parent = panel
+
+				-- First-run dead end: a field that points at authored content is useless until some
+				-- exists, and the picker simply isn't there to hint at it. Say where to go, and
+				-- offer to take them.
+				if spec.ref and (not choices or #choices == 0) then
+					local cat = ContentAdmin.CATEGORIES and ContentAdmin.CATEGORIES[spec.ref]
+					local catTitle = (cat and cat.title) or spec.ref
+					local jump = Theme.button({
+						Size = UDim2.new(1, 0, 0, 22),
+						Text = `No {catTitle} yet — create one →`,
+						TextColor3 = Theme.COLOR.ACCENT,
+						TextSize = 11,
+						LayoutOrder = i,
+					})
+					jump.Parent = panel
+					jump.MouseButton1Click:Connect(function()
+						if actions.selectPage then
+							actions.selectPage("content/" .. spec.ref)
+						end
+					end)
+				end
 			end
 		end
 

plugin/init.server.luau

@@ -138,6 +138,13 @@ local buildActions = {
 			return BuildAdmin.resetField(instance, spec)
 		end)
 	end,
+	-- Not a mutation (no recording): jump to a Content page so a field that references authored
+	-- content can send a first-time creator somewhere useful instead of dead-ending.
+	selectPage = function(id: string)
+		if nav then
+			nav.selectPage(id)
+		end
+	end,
 }
 
 -- ── Content callbacks (authored + overrides), bundled for the pages ──────────