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/__snapshots__/tool.test.ts.snap

@@ -0,0 +1,9 @@
+// Bun Snapshot v1, https://bun.sh/docs/test/snapshots
+
+exports[`tool.ls basic 1`] = `
+"packages/opencode/test/fixtures/example/
+  broken.ts
+  cli.ts
+  ink.tsx
+"
+`;