Adds oembed redirect and a home for more redirects

[eyeseast]

I saw 404s on /api/oembed.json/, so this ensures we normalize the URL and redirect correctly. Once this merges, we can remove the version in the CF dashboard.

I also added a (redirects) directory so these stay in one place and don't clutter up other routes. The /app redirect is there now.

[github-actions]

Preview deployed: https://preview-1319.staging.documentcloud.org

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	58.57%	2380 / 4063
🔵	Statements	59.17%	2756 / 4657
🔵	Functions	60.52%	621 / 1026
🔵	Branches	59.34%	1460 / 2460

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
src/routes/(redirects)/api/oembed.json/+server.ts	0%	100%	0%	0%	4-11

Generated in workflow #1200 for commit 9797080 by the Vitest Coverage Report Action

[duckduckgrayduck]

I've confirmed that

• /app and /app/ redirect to /documents/
• /api/oembed.json/ redirects to /api/oembed/

I can't seem to test if /api/oembed.json with a URL parameter redirects or not, because the front-end assets are a different link than the documents on the backend

[eyeseast]

I confirmed that this forwards query params: https://preview-1319.staging.documentcloud.org/api/oembed.json?url=https://preview-1319.staging.documentcloud.org/documents/20011330-pioservices/

The staging server doesn't recognize the domain, so it 404s, but that's fine.

[duckduckgrayduck]

Yea, that's basically what I was getting at, otherwise looks good