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/storage/db.test.ts

@@ -0,0 +1,19 @@
+import { describe, expect, test } from "bun:test"
+import path from "path"
+import { Global } from "../../src/global"
+import { Installation } from "../../src/installation"
+import { Database } from "../../src/storage/db"
+
+describe("Database.Path", () => {
+  test("returns database path for the current channel", () => {
+    const db = process.env["OPENCODE_DB"]
+    const expected = db
+      ? path.isAbsolute(db)
+        ? db
+        : path.join(Global.Path.data, db)
+      : ["latest", "beta"].includes(Installation.CHANNEL)
+        ? path.join(Global.Path.data, "opencode.db")
+        : path.join(Global.Path.data, `opencode-${Installation.CHANNEL.replace(/[^a-zA-Z0-9._-]/g, "-")}.db`)
+    expect(Database.Path).toBe(expected)
+  })
+})