refactor: apply minimal tfcode branding

- Rename packages/opencode → packages/tfcode (directory only)
- Rename bin/opencode → bin/tfcode (CLI binary)
- Rename .opencode → .tfcode (config directory)
- Update package.json name and bin field
- Update config directory path references (.tfcode)
- Keep internal code references as 'opencode' for easy upstream sync
- Keep @opencode-ai/* workspace package names

This minimal branding approach allows clean merges from upstream
opencode repository while providing tfcode branding for users.

packages/tfcode/test/tool/registry.test.ts

@@ -0,0 +1,126 @@
+import { afterEach, describe, expect, test } from "bun:test"
+import path from "path"
+import fs from "fs/promises"
+import { tmpdir } from "../fixture/fixture"
+import { Instance } from "../../src/project/instance"
+import { ToolRegistry } from "../../src/tool/registry"
+
+afterEach(async () => {
+  await Instance.disposeAll()
+})
+
+describe("tool.registry", () => {
+  test("loads tools from .opencode/tool (singular)", async () => {
+    await using tmp = await tmpdir({
+      init: async (dir) => {
+        const opencodeDir = path.join(dir, ".opencode")
+        await fs.mkdir(opencodeDir, { recursive: true })
+
+        const toolDir = path.join(opencodeDir, "tool")
+        await fs.mkdir(toolDir, { recursive: true })
+
+        await Bun.write(
+          path.join(toolDir, "hello.ts"),
+          [
+            "export default {",
+            "  description: 'hello tool',",
+            "  args: {},",
+            "  execute: async () => {",
+            "    return 'hello world'",
+            "  },",
+            "}",
+            "",
+          ].join("\n"),
+        )
+      },
+    })
+
+    await Instance.provide({
+      directory: tmp.path,
+      fn: async () => {
+        const ids = await ToolRegistry.ids()
+        expect(ids).toContain("hello")
+      },
+    })
+  })
+
+  test("loads tools from .opencode/tools (plural)", async () => {
+    await using tmp = await tmpdir({
+      init: async (dir) => {
+        const opencodeDir = path.join(dir, ".opencode")
+        await fs.mkdir(opencodeDir, { recursive: true })
+
+        const toolsDir = path.join(opencodeDir, "tools")
+        await fs.mkdir(toolsDir, { recursive: true })
+
+        await Bun.write(
+          path.join(toolsDir, "hello.ts"),
+          [
+            "export default {",
+            "  description: 'hello tool',",
+            "  args: {},",
+            "  execute: async () => {",
+            "    return 'hello world'",
+            "  },",
+            "}",
+            "",
+          ].join("\n"),
+        )
+      },
+    })
+
+    await Instance.provide({
+      directory: tmp.path,
+      fn: async () => {
+        const ids = await ToolRegistry.ids()
+        expect(ids).toContain("hello")
+      },
+    })
+  })
+
+  test("loads tools with external dependencies without crashing", async () => {
+    await using tmp = await tmpdir({
+      init: async (dir) => {
+        const opencodeDir = path.join(dir, ".opencode")
+        await fs.mkdir(opencodeDir, { recursive: true })
+
+        const toolsDir = path.join(opencodeDir, "tools")
+        await fs.mkdir(toolsDir, { recursive: true })
+
+        await Bun.write(
+          path.join(opencodeDir, "package.json"),
+          JSON.stringify({
+            name: "custom-tools",
+            dependencies: {
+              "@opencode-ai/plugin": "^0.0.0",
+              cowsay: "^1.6.0",
+            },
+          }),
+        )
+
+        await Bun.write(
+          path.join(toolsDir, "cowsay.ts"),
+          [
+            "import { say } from 'cowsay'",
+            "export default {",
+            "  description: 'tool that imports cowsay at top level',",
+            "  args: { text: { type: 'string' } },",
+            "  execute: async ({ text }: { text: string }) => {",
+            "    return say({ text })",
+            "  },",
+            "}",
+            "",
+          ].join("\n"),
+        )
+      },
+    })
+
+    await Instance.provide({
+      directory: tmp.path,
+      fn: async () => {
+        const ids = await ToolRegistry.ids()
+        expect(ids).toContain("cowsay")
+      },
+    })
+  })
+})