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/config/fixtures/empty-frontmatter.md

@@ -0,0 +1,4 @@
+---
+---
+
+Content

packages/tfcode/test/config/fixtures/frontmatter.md

@@ -0,0 +1,28 @@
+---
+description: "This is a description wrapped in quotes"
+# field: this is a commented out field that should be ignored
+occupation: This man has the following occupation: Software Engineer
+title: 'Hello World'
+name: John "Doe"
+
+family: He has no 'family'
+summary: >
+  This is a summary
+url: https://example.com:8080/path?query=value
+time: The time is 12:30:00 PM
+nested: First: Second: Third: Fourth
+quoted_colon: "Already quoted: no change needed"
+single_quoted_colon: 'Single quoted: also fine'
+mixed: He said "hello: world" and then left
+empty:
+dollar: Use $' and $& for special patterns
+---
+
+Content that should not be parsed:
+
+fake_field: this is not yaml
+another: neither is this
+time: 10:30:00 AM
+url: https://should-not-be-parsed.com:3000
+
+The above lines look like YAML but are just content.

packages/tfcode/test/config/fixtures/markdown-header.md

@@ -0,0 +1,11 @@
+# Response Formatting Requirements
+
+Always structure your responses using clear markdown formatting:
+
+- By default don't put information into tables for questions (but do put information into tables when creating or updating files)
+- Use headings (##, ###) to organise sections, always
+- Use bullet points or numbered lists for multiple items
+- Use code blocks with language tags for any code
+- Use **bold** for key terms and emphasis
+- Use tables when comparing options or listing structured data
+- Break long responses into logical sections with headings

packages/tfcode/test/config/fixtures/no-frontmatter.md

@@ -0,0 +1 @@
+Content

packages/tfcode/test/config/fixtures/weird-model-id.md

@@ -0,0 +1,13 @@
+---
+description: General coding and planning agent
+mode: subagent
+model: synthetic/hf:zai-org/GLM-4.7
+tools:
+  write: true
+  read: true
+  edit: true
+stuff: >
+  This is some stuff
+---
+
+Strictly follow da rules