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/issues.md

@@ -0,0 +1,23 @@
+---
+description: "find issue(s) on github"
+model: opencode/claude-haiku-4-5
+---
+
+Search through existing issues in anomalyco/opencode using the gh cli to find issues matching this query:
+
+$ARGUMENTS
+
+Consider:
+
+1. Similar titles or descriptions
+2. Same error messages or symptoms
+3. Related functionality or components
+4. Similar feature requests
+
+Please list any matching issues with:
+
+- Issue number and title
+- Brief explanation of why it matches the query
+- Link to the issue
+
+If no clear matches are found, say so.