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.

.tfcode/command/rmslop.md

@@ -0,0 +1,15 @@
+---
+description: Remove AI code slop
+---
+
+Check the diff against dev, and remove all AI generated slop introduced in this branch.
+
+This includes:
+
+- Extra comments that a human wouldn't add or is inconsistent with the rest of the file
+- Extra defensive checks or try/catch blocks that are abnormal for that area of the codebase (especially if called by trusted / validated codepaths)
+- Casts to any to get around type issues
+- Any other style that is inconsistent with the file
+- Unnecessary emoji usage
+
+Report at the end with only a 1-3 sentence summary of what you changed