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/server/session-select.test.ts

@@ -0,0 +1,78 @@
+import { describe, expect, test } from "bun:test"
+import path from "path"
+import { Session } from "../../src/session"
+import { Log } from "../../src/util/log"
+import { Instance } from "../../src/project/instance"
+import { Server } from "../../src/server/server"
+
+const projectRoot = path.join(__dirname, "../..")
+Log.init({ print: false })
+
+describe("tui.selectSession endpoint", () => {
+  test("should return 200 when called with valid session", async () => {
+    await Instance.provide({
+      directory: projectRoot,
+      fn: async () => {
+        // #given
+        const session = await Session.create({})
+
+        // #when
+        const app = Server.Default()
+        const response = await app.request("/tui/select-session", {
+          method: "POST",
+          headers: { "Content-Type": "application/json" },
+          body: JSON.stringify({ sessionID: session.id }),
+        })
+
+        // #then
+        expect(response.status).toBe(200)
+        const body = await response.json()
+        expect(body).toBe(true)
+
+        await Session.remove(session.id)
+      },
+    })
+  })
+
+  test("should return 404 when session does not exist", async () => {
+    await Instance.provide({
+      directory: projectRoot,
+      fn: async () => {
+        // #given
+        const nonExistentSessionID = "ses_nonexistent123"
+
+        // #when
+        const app = Server.Default()
+        const response = await app.request("/tui/select-session", {
+          method: "POST",
+          headers: { "Content-Type": "application/json" },
+          body: JSON.stringify({ sessionID: nonExistentSessionID }),
+        })
+
+        // #then
+        expect(response.status).toBe(404)
+      },
+    })
+  })
+
+  test("should return 400 when session ID format is invalid", async () => {
+    await Instance.provide({
+      directory: projectRoot,
+      fn: async () => {
+        // #given
+        const invalidSessionID = "invalid_session_id"
+
+        // #when
+        const app = Server.Default()
+        const response = await app.request("/tui/select-session", {
+          method: "POST",
+          headers: { "Content-Type": "application/json" },
+          body: JSON.stringify({ sessionID: invalidSessionID }),
+        })
+
+        // #then
+        expect(response.status).toBe(400)
+      },
+    })
+  })
+})