Add read-only terminal portfolio filesystem

[cursor]

Issue

Problem

The terminal interface exposed pwd/cd placeholders and ls only listed commands, which limited the site’s terminal-emulation goal.

Proposed solution

Add a generated, read-only /home/guest portfolio filesystem backed by existing site JSON data.

Acceptance criteria

• pwd prints the current virtual directory.
• ls [path] lists filesystem entries, with ls --commands preserving the command index.
• cd [path] supports relative paths, absolute paths, ~, ., and ...
• cat [file] reads generated portfolio files.
• tree [path] renders recursive directory trees.
• Tab completion includes filesystem paths for cd, cat, ls, and tree.

Changes

• Added virtual filesystem helpers and path resolution utilities in src/lib/terminal/index.js.
• Wired pwd, ls, cd, cat, and tree into the terminal runtime with path-aware prompts.
• Added unit coverage for filesystem generation, traversal, errors, tree output, and completions.
• Documented the terminal filesystem in README.md.

Verification

• Pre-push npm run check passed: lint, format check, coverage tests, and Astro build.