docs: add "How to Back Up Data from Akash Apps" community guide

[listersb]

Summary

Adds a new community contribution, How to Back Up Data from Akash Apps, at src/content/Community_Contributions_Page/how-to-back-up-data-from-akash-apps/. Authored by Sam Lister.

The guide covers:

• Why storage on Akash is currently ephemeral by default, and how persistent storage fits in (and where it stops being enough)
• Why there's no built-in one-click file download, and when SSH/shell access is and isn't available
• Two application-level approaches to backups (expose a download endpoint vs. push data out from the app)
• A curated list of working community backup examples (Postgres, MongoDB, MariaDB, Redis, CouchDB → Storj / Dropbox / Apillon)

Banner

Includes a new project-banner.png (1920×1080, matching the other contribution banners' dimensions) in an atmospheric style inspired by the AkashML hero image — minimal title, Akash red mark.

Verification

• npm run build passes locally (591 pages); page renders at dist/community/contributions/how-to-back-up-data-from-akash-apps/index.html.
• Frontmatter validates against communityContributionsSchema (src/utils/schema/communityContributions.ts). No link: field, since this is original-to-site content (matching cloud-war/index.md).
• All 10 external links resolve (verified): the 8 community repos, plus the Akash Discord and support form (both HTTP 200).
• Visual check of the rendered page confirms banner, byline, headings, and both lists display correctly.

Test plan

• CI build passes.
• Page renders at /community/contributions/how-to-back-up-data-from-akash-apps/ with the banner.
• Entry appears on the /community/contributions/ index, sorted by pubDate.
• Author shows as "Sam Lister".

Note: four of the community example links point to a branch inside a fork (…/awesome-akash/tree/<branch>/…); all resolve at time of writing.

[HoomanDgtl]

hii @Zblocker64 , this PR is good to merge.