chore: migrate tests from tests-ui/ to colocate with source files (#7811)

## Summary

Migrates all unit tests from `tests-ui/` to colocate with their source
files in `src/`, improving discoverability and maintainability.

## Changes

- **What**: Relocated all unit tests to be adjacent to the code they
test, following the `<source>.test.ts` naming convention
- **Config**: Updated `vitest.config.ts` to remove `tests-ui` include
pattern and `@tests-ui` alias
- **Docs**: Moved testing documentation to `docs/testing/` with updated
paths and patterns

## Review Focus

- Migration patterns documented in
`temp/plans/migrate-tests-ui-to-src.md`
- Tests use `@/` path aliases instead of relative imports
- Shared fixtures placed in `__fixtures__/` directories

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7811-chore-migrate-tests-from-tests-ui-to-colocate-with-source-files-2da6d73d36508147a4cce85365dee614)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: GitHub Action <action@github.com>

src/composables/node/usePriceBadge.test.ts

@@ -0,0 +1,57 @@
+import { describe, expect, vi } from 'vitest'
+
+import { LGraphNode } from '@/lib/litegraph/src/litegraph'
+
+import { subgraphTest } from '@/lib/litegraph/src/subgraph/__fixtures__/subgraphFixtures'
+
+import { usePriceBadge } from '@/composables/node/usePriceBadge'
+
+vi.mock('@/stores/workspace/colorPaletteStore', () => ({
+  useColorPaletteStore: () => ({
+    completedActivePalette: {
+      light_theme: false,
+      colors: { litegraph_base: {} }
+    }
+  })
+}))
+
+const { updateSubgraphCredits, getCreditsBadge } = usePriceBadge()
+
+const mockNode = new LGraphNode('mock node')
+mockNode.badges = [getCreditsBadge('$0.05/Run')]
+
+function getBadgeText(node: LGraphNode): string {
+  const badge = node.badges[0]
+  return (typeof badge === 'function' ? badge() : badge).text
+}
+
+describe('subgraph pricing', () => {
+  subgraphTest(
+    'should not display badge for subgraphs without API nodes',
+    ({ subgraphWithNode }) => {
+      const { subgraphNode } = subgraphWithNode
+      updateSubgraphCredits(subgraphNode)
+      expect(subgraphNode.badges.length).toBe(0)
+    }
+  )
+  subgraphTest(
+    'should return the price of a single contained API node',
+    ({ subgraphWithNode }) => {
+      const { subgraphNode, subgraph } = subgraphWithNode
+      subgraph.add(mockNode)
+      updateSubgraphCredits(subgraphNode)
+      expect(subgraphNode.badges.length).toBe(1)
+      expect(getBadgeText(subgraphNode)).toBe('$0.05/Run')
+    }
+  )
+  subgraphTest(
+    'should return the number of api nodes if more than one exists',
+    ({ subgraphWithNode }) => {
+      const { subgraphNode, subgraph } = subgraphWithNode
+      for (let i = 0; i < 5; i++) subgraph.add(mockNode)
+      updateSubgraphCredits(subgraphNode)
+      expect(subgraphNode.badges.length).toBe(1)
+      expect(getBadgeText(subgraphNode)).toBe('Partner Nodes x 5')
+    }
+  )
+})