chore: host EMQX SL cert directory at /emqxsl-cert/

[mikestankavich]

What

Stage a cert directory the GL-S10 beacon scanner can be pointed at.

• Base URL for the device: https://docs.trakrf.id/emqxsl-cert/ (preview: https://docs.preview.trakrf.id/emqxsl-cert/)
• The device appends ca.crt / client.crt / client.key to that base itself.

File	Content
ca.crt	EMQX SL CA — DigiCert Global Root G2, from https://assets.emqx.com/data/emqxsl-ca.crt
client.crt	empty placeholder
client.key	empty placeholder

Why this layout

The GL-S10 firmware takes a base directory URL and auto-fetches fixed filenames — it rejects a direct file URL. A previous attempt (#185) placed a single ca.crt and was closed; this re-does it as the directory pattern the firmware actually expects.

Notes

• EMQX SL Serverless authenticates with username/password over server-auth TLS, not mutual TLS — so only ca.crt carries real content.
• client.crt / client.key are empty placeholders, for firmware that wants all three paths to return 200. Empty by design: no private key is ever published. If the device requires a valid client key, that's real mTLS and cannot be solved by public hosting.
• Unverified: whether the GL-S10 cert-download accepts HTTPS. Cloudflare Pages 301s HTTP→HTTPS, so if the firmware only speaks plain HTTP this won't work regardless of layout. Pointing the device at the preview URL and reading the actual error is the way to confirm.
• Static-asset-only change — no doc content or config touched.

🤖 Generated with Claude Code

[github-actions]

🚀 Preview Deployment Update

✅ This PR has been successfully merged into the preview branch.

The preview environment will update shortly at: https://docs.preview.trakrf.id

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[mikestankavich]

Closing — superseded by the MQTT broker migration from EMQX SL Serverless to Mosquitto on GKE. This PR hosted the EMQX SL CA (DigiCert Global Root G2) at /emqxsl-cert/ so the GL-S10 firmware could trust the EMQX SL broker's TLS. With the broker moving to Mosquitto-on-GKE, that CA is for the wrong endpoint, and the GKE broker's TLS is publicly-trusted (no hosted CA needed for the device). Never validated against a real device (the "does the GL-S10 accept HTTPS" question was left open). If a future broker turns out to need a privately-rooted CA hosted for the device, re-open with the new CA rather than this one.