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/ide/ide.test.ts

@@ -0,0 +1,82 @@
+import { describe, expect, test, afterEach } from "bun:test"
+import { Ide } from "../../src/ide"
+
+describe("ide", () => {
+  const original = { ...process.env }
+
+  afterEach(() => {
+    Object.keys(process.env).forEach((key) => {
+      delete process.env[key]
+    })
+    Object.assign(process.env, original)
+  })
+
+  test("should detect Visual Studio Code", () => {
+    process.env["TERM_PROGRAM"] = "vscode"
+    process.env["GIT_ASKPASS"] = "/path/to/Visual Studio Code.app/Contents/Resources/app/extensions/git/dist/askpass.sh"
+
+    expect(Ide.ide()).toBe("Visual Studio Code")
+  })
+
+  test("should detect Visual Studio Code Insiders", () => {
+    process.env["TERM_PROGRAM"] = "vscode"
+    process.env["GIT_ASKPASS"] =
+      "/Applications/Visual Studio Code - Insiders.app/Contents/Resources/app/extensions/git/dist/askpass.sh"
+
+    expect(Ide.ide()).toBe("Visual Studio Code - Insiders")
+  })
+
+  test("should detect Cursor", () => {
+    process.env["TERM_PROGRAM"] = "vscode"
+    process.env["GIT_ASKPASS"] = "/path/to/Cursor.app/Contents/Resources/app/extensions/git/dist/askpass.sh"
+
+    expect(Ide.ide()).toBe("Cursor")
+  })
+
+  test("should detect VSCodium", () => {
+    process.env["TERM_PROGRAM"] = "vscode"
+    process.env["GIT_ASKPASS"] = "/path/to/VSCodium.app/Contents/Resources/app/extensions/git/dist/askpass.sh"
+
+    expect(Ide.ide()).toBe("VSCodium")
+  })
+
+  test("should detect Windsurf", () => {
+    process.env["TERM_PROGRAM"] = "vscode"
+    process.env["GIT_ASKPASS"] = "/path/to/Windsurf.app/Contents/Resources/app/extensions/git/dist/askpass.sh"
+
+    expect(Ide.ide()).toBe("Windsurf")
+  })
+
+  test("should return unknown when TERM_PROGRAM is not vscode", () => {
+    process.env["TERM_PROGRAM"] = "iTerm2"
+    process.env["GIT_ASKPASS"] =
+      "/Applications/Visual Studio Code - Insiders.app/Contents/Resources/app/extensions/git/dist/askpass.sh"
+
+    expect(Ide.ide()).toBe("unknown")
+  })
+
+  test("should return unknown when GIT_ASKPASS does not contain IDE name", () => {
+    process.env["TERM_PROGRAM"] = "vscode"
+    process.env["GIT_ASKPASS"] = "/path/to/unknown/askpass.sh"
+
+    expect(Ide.ide()).toBe("unknown")
+  })
+
+  test("should recognize vscode-insiders OPENCODE_CALLER", () => {
+    process.env["OPENCODE_CALLER"] = "vscode-insiders"
+
+    expect(Ide.alreadyInstalled()).toBe(true)
+  })
+
+  test("should recognize vscode OPENCODE_CALLER", () => {
+    process.env["OPENCODE_CALLER"] = "vscode"
+
+    expect(Ide.alreadyInstalled()).toBe(true)
+  })
+
+  test("should return false for unknown OPENCODE_CALLER", () => {
+    process.env["OPENCODE_CALLER"] = "unknown"
+
+    expect(Ide.alreadyInstalled()).toBe(false)
+  })
+})