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/learn.md

@@ -0,0 +1,42 @@
+---
+description: Extract non-obvious learnings from session to AGENTS.md files to build codebase understanding
+---
+
+Analyze this session and extract non-obvious learnings to add to AGENTS.md files.
+
+AGENTS.md files can exist at any directory level, not just the project root. When an agent reads a file, any AGENTS.md in parent directories are automatically loaded into the context of the tool read. Place learnings as close to the relevant code as possible:
+
+- Project-wide learnings → root AGENTS.md
+- Package/module-specific → packages/foo/AGENTS.md
+- Feature-specific → src/auth/AGENTS.md
+
+What counts as a learning (non-obvious discoveries only):
+
+- Hidden relationships between files or modules
+- Execution paths that differ from how code appears
+- Non-obvious configuration, env vars, or flags
+- Debugging breakthroughs when error messages were misleading
+- API/tool quirks and workarounds
+- Build/test commands not in README
+- Architectural decisions and constraints
+- Files that must change together
+
+What NOT to include:
+
+- Obvious facts from documentation
+- Standard language/framework behavior
+- Things already in an AGENTS.md
+- Verbose explanations
+- Session-specific details
+
+Process:
+
+1. Review session for discoveries, errors that took multiple attempts, unexpected connections
+2. Determine scope - what directory does each learning apply to?
+3. Read existing AGENTS.md files at relevant levels
+4. Create or update AGENTS.md at the appropriate level
+5. Keep entries to 1-3 lines per insight
+
+After updating, summarize which AGENTS.md files were created/updated and how many learnings per file.
+
+$ARGUMENTS