Add read-only virtual terminal filesystem

[cursor]

Issue

Title

Add portfolio-backed filesystem commands to the terminal

Problem

The site is moving toward terminal emulation, but pwd was fixed to /home/guest, cd did not maintain real state, and ls only listed commands. Visitors could not browse portfolio content with familiar shell filesystem commands.

Proposed improvement

Generate a read-only virtual /home/guest filesystem from the existing JSON data and wire shell-like commands into the terminal runtime.

Acceptance criteria

• pwd reflects the current virtual directory.
• ls [path] lists virtual files and directories, while ls --commands preserves command discovery.
• cd [path] supports relative paths, absolute paths, ~, ., and ...
• cat [path] prints generated portfolio files.
• tree [path] renders a bounded directory tree.
• Unit tests cover path normalization, generated content, directory/file errors, duplicate filenames, and tree output.

Changes

• Added virtual filesystem helpers in src/lib/terminal/index.js.
• Added cat and tree commands plus path-aware pwd, cd, and ls behavior in src/scripts/terminal.js.
• Updated help/man text and README documentation for filesystem commands.
• Added focused Vitest coverage for filesystem generation and edge cases.

Validation

• Pre-push npm run check passed: lint, format check, 70 unit tests with 85.56% branch coverage, and Astro build.