fix: accept flexible author field formats in PR description

[SSoggyTacoMan]

Fixes several issues with the auto-triage bot that were causing false failures and confusing error messages.

Changes

Flexible author field parsing
The bot only matched **Author:** in bold. Submitters using @mentions, markdown links, unbolded Author: name, or heading-style formatting kept failing even with valid info filled in.
Now accepts all of: **Author:** name, **Author:** @mention, [@foo](github url), Author: name (unbolded), ### Author name\nAuthor: name.

No cascading errors from bad filename
When a filename had invalid characters (e.g. an apostrophe in Rayan's-Maze.js), the bot would report 3 separate failures: invalid filename, no game file found, and metadata not checked — even though there was one game file and it was in the right place. Now only the filename check fails; the file is still recognized for count and metadata purposes. The materializeSubmittedGameFiles function now also uses a loose regex so badly named files are actually fetched and validated.

Better filename error message
Was: "Filenames cannot contain spaces."
Now: "Filenames may only contain letters, numbers, hyphens, and underscores (no spaces, apostrophes, or special characters)."

Better check name
"Files stay in allowed folders" → "Valid filenames and folders" (the old name was confusing when the file was in the right folder but had a bad name).

Duplicate open PR detection
Now detects when the same GitHub user already has another open submission PR, regardless of filename validity or game title match. Only counts PRs with the Submission label so valid submissions aren't blocked if the user has an open non-game PR (e.g. a docs fix). When a duplicate PR is closed, the bot will now automatically re-validate the remaining open PR from that user so it escapes the "Failed" state.

Optimized title conflict check
The existing check fetched file diffs for every open PR in the entire repository. It now filters candidates to only PRs with the Submission label, saving massive amounts of API calls and preventing rate limits.

Tutorial game detection
Detects if the submitted game is an unmodified getting_started.js or maze_game_starter.js by comparing stripped code bodies, and fails with a clear message.

Open preview and PR comment links in new tab
Links in the auto-triage bot comment (including "Play in Sprig Editor", "Edit Game File", "Play Similar Game (Gallery)", "View Raw", "View Screenshot", and "PR Files") now open in a new tab (target="_blank" rel="noopener noreferrer") so reviewers and authors do not lose their place on the pull request.

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[SSoggyTacoMan]

Bug in duplicate PR detection. openPulls.find checks for any open PR by the user. If they have an open PR for an engine typo fix, it incorrectly blocks their game submission.

Fix: filter by the 'Submission' label.

const duplicatePR = openPulls.find((pr) => 
	pr.number !== prNumber && 
	pr.user?.login === submitterLogin && 
	pr.labels?.some(l => l.name === 'Submission')
);