fix: support absolute paths in Output and Screenshot commands

[tmchow]

Summary

Output /tmp/demo.gif fails with parser errors because the lexer treats / as a regex delimiter. The path /tmp/demo.gif tokenizes as REGEX("tmp") + STRING("demo.gif") instead of a single path token, and parseOutput() rejects the unexpected REGEX.

This also breaks the template that vhs new generates, which uses an absolute Output path.

Fixes #741

Root Cause

In lexer/lexer.go, case '/' always creates a REGEX token via readRegex('/'). The parser expects STRING after Output but sees REGEX, producing: "Expected file path after output."

The fix is in the parser, not the lexer. The / character is genuinely ambiguous (regex vs path), but the parser knows the context: after Output/Screenshot, a path is expected. After Wait, a regex is expected.

Changes

Added parsePathArgument() in parser/parser.go that accepts both STRING tokens (relative paths, existing behavior) and REGEX + STRING sequences (absolute paths like /tmp/demo.gif). Both parseOutput() and parseScreenshot() use this shared helper.

Testing

Added TestParseAbsolutePaths covering:

• Output /tmp/demo.gif (absolute GIF)
• Output /tmp/demo.mp4 (absolute MP4)
• Output /home/user/recordings/demo.webm (deep absolute path)
• Output /frames/ (absolute directory output)
• Output examples/out.gif (relative path, unchanged)
• Output frames/ (relative directory, unchanged)
• Screenshot /tmp/screenshot.png (absolute screenshot)
• Screenshot examples/screenshot.png (relative screenshot, unchanged)

All 51 existing tests pass. go vet and gofumpt clean.

Before

$ vhs new test.tape && vhs test.tape

 60 │ Output /tmp/test.gif
      ^^^^^^ Expected file path after output
 60 │ Output /tmp/test.gif
             ^^^ Invalid command: tmp

parser: 3 error(s)

After

$ vhs new test.tape && vhs test.tape
Creating /tmp/test.gif...

Note: This contribution was developed with AI assist w/ Codex.