docs: add security scan page for reflex cloud scan

[adhami3310]

Adds a docs page for the reflex cloud scan security review command (#6632).

• New page docs/hosting/security-scan.md: running a scan, reading results by severity, --fail-on gating, JSON output, and a GitHub Actions CI example.
• Registers scan in the CLI reference categories so /docs/hosting/cli/scan/ is auto-generated from the command help.
• Adds the page to the hosting sidebar under the App section.

[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing docs/security-scan (d27a896) with main (785db92)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[greptile-apps]

Greptile Summary

This PR adds documentation for the reflex cloud scan security review command introduced in #6632. All three changed files are purely additive and documentation-only.

• docs/hosting/security-scan.md: New page covering usage, severity levels, --fail-on gating, JSON output, and a GitHub Actions CI example. Verified against scan.py: all flags (--fail-on, --json/-j, --no-interactive, --token), their defaults, and the exit-code logic are accurately described.
• cloud_cliref.py: Registers "scan" under REFLEX_CLOUD_PREFIX so the auto-generated CLI reference appears at /docs/hosting/cli/scan/; the command is correctly wired in deployments.py.
• learn.py: Adds the new page to the hosting sidebar's "App" group, sensibly positioned between the tokens page and the GitHub Actions deployment guide.

Confidence Score: 5/5

Documentation-only change with no runtime code paths affected; safe to merge.

All three files are additive docs changes. The new page's claims were verified against the scan.py implementation — flags, defaults, severity ordering, and exit-code behaviour all match exactly. The sidebar and CLI-reference wiring follow the same patterns used by every other hosting page.

No files require special attention.

Important Files Changed

Filename	Overview
docs/hosting/security-scan.md	New docs page for reflex cloud scan; content is accurate against the implementation in scan.py — flags, defaults, and behavior all match.
docs/app/reflex_docs/pages/docs/cloud_cliref.py	Adds "scan" to the CLI-reference categories dict under REFLEX_CLOUD_PREFIX; correctly maps to "reflex cloud scan" which is registered in deployments.py.
docs/app/reflex_docs/templates/docpage/sidebar/sidebar_items/learn.py	Adds hosting.security_scan to the "App" sidebar group, placed logically between the tokens page and the GitHub Actions deployment guide.

_{Reviews (2): Last reviewed commit: "docs: correct scan output description pe..." | Re-trigger Greptile}