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/util/format.test.ts

@@ -0,0 +1,59 @@
+import { describe, expect, test } from "bun:test"
+import { formatDuration } from "../../src/util/format"
+
+describe("util.format", () => {
+  describe("formatDuration", () => {
+    test("returns empty string for zero or negative values", () => {
+      expect(formatDuration(0)).toBe("")
+      expect(formatDuration(-1)).toBe("")
+      expect(formatDuration(-100)).toBe("")
+    })
+
+    test("formats seconds under a minute", () => {
+      expect(formatDuration(1)).toBe("1s")
+      expect(formatDuration(30)).toBe("30s")
+      expect(formatDuration(59)).toBe("59s")
+    })
+
+    test("formats minutes under an hour", () => {
+      expect(formatDuration(60)).toBe("1m")
+      expect(formatDuration(61)).toBe("1m 1s")
+      expect(formatDuration(90)).toBe("1m 30s")
+      expect(formatDuration(120)).toBe("2m")
+      expect(formatDuration(330)).toBe("5m 30s")
+      expect(formatDuration(3599)).toBe("59m 59s")
+    })
+
+    test("formats hours under a day", () => {
+      expect(formatDuration(3600)).toBe("1h")
+      expect(formatDuration(3660)).toBe("1h 1m")
+      expect(formatDuration(7200)).toBe("2h")
+      expect(formatDuration(8100)).toBe("2h 15m")
+      expect(formatDuration(86399)).toBe("23h 59m")
+    })
+
+    test("formats days under a week", () => {
+      expect(formatDuration(86400)).toBe("~1 day")
+      expect(formatDuration(172800)).toBe("~2 days")
+      expect(formatDuration(259200)).toBe("~3 days")
+      expect(formatDuration(604799)).toBe("~6 days")
+    })
+
+    test("formats weeks", () => {
+      expect(formatDuration(604800)).toBe("~1 week")
+      expect(formatDuration(1209600)).toBe("~2 weeks")
+      expect(formatDuration(1609200)).toBe("~2 weeks")
+    })
+
+    test("handles boundary values correctly", () => {
+      expect(formatDuration(59)).toBe("59s")
+      expect(formatDuration(60)).toBe("1m")
+      expect(formatDuration(3599)).toBe("59m 59s")
+      expect(formatDuration(3600)).toBe("1h")
+      expect(formatDuration(86399)).toBe("23h 59m")
+      expect(formatDuration(86400)).toBe("~1 day")
+      expect(formatDuration(604799)).toBe("~6 days")
+      expect(formatDuration(604800)).toBe("~1 week")
+    })
+  })
+})