500 Internal Server Error when adding custom domain to Site (Appwrite Cloud SGP)

### 👟 Reproduction steps

When trying to add a custom domain to an Appwrite Site in the Singapore Cloud region, the request to create the site rule fails with a 500 Internal Server Error. The Appwrite‑provided default domain works, but adding my own domain consistently fails.

Steps to Reproduce
Log into Appwrite Cloud and select my project in the Singapore (SGP) region.

Go to Sites → [my site] → Domains.

Click Add domain.

Enter a custom subdomain, for example: waflow.krtrim.tech (no protocol, no slash).

Choose rule type: Active deployment.

Select the available server/region (SGP).

Click Add.

### 👍 Expected behavior

Domain is created successfully.

Appwrite returns the DNS record (CNAME) to add at my DNS provider.

No server error is shown in the console.

### 👎 Actual Behavior

A toast appears in the Appwrite Console indicating a server error.

The domain is not added to the Site.

- The browser console shows repeated 500 errors from the Sites proxy rule endpoint.
```
sgp.cloud.appwrite.io/v1/proxy/rules/site:1 Failed to load resource: the server responded with a status of 500 ()
sgp.cloud.appwrite.io/v1/proxy/rules/site:1 Failed to load resource: the server responded with a status of 500 ()
sgp.cloud.appwrite.io/v1/proxy/rules/site:1 Failed to load resource: the server responded with a status of 500 ()
sgp.cloud.appwrite.io/v1/proxy/rules/site:1 Failed to load resource: the server responded with a status of 500 ()
sgp.cloud.appwrite.io/v1/proxy/rules/site:1 Failed to load resource: the server responded with a status of 500 ()

+page.svelte:106 POST https://sgp.cloud.appwrite.io/v1/proxy/rules/site 500 (Internal Server Error)
window.fetch @ fetcher.js:76
(anonymous) @ fetch.js:75
(anonymous) @ sdk.js:868
(anonymous) @ sdk.js:22
H @ sdk.js:18
call @ sdk.js:865
createSiteRule @ sdk.js:17533
Le @ +page.svelte:106
d @ form.svelte:35
(anonymous) @ event-modifiers.js:98
(anonymous) @ events.js:66
bt @ shared.js:44
a @ events.js:65
r @ helpers.js:93
u @ form.svelte:30
click @ +page.svelte:269
A @ misc.js:39
Ni.$$events.click @ button.svelte:114
A @ misc.js:39
(anonymous) @ Button.svelte:29
(anonymous) @ events.js:66
bt @ shared.js:44
a @ events.js:65
r @ helpers.js:93
```

### 🎲 Appwrite version

Appwrite Cloud

### 💻 Operating system

Linux

### 🧱 Your Environment

Platform: Appwrite Cloud

Region: Singapore (sgp.cloud.appwrite.io)

Product: Sites → Domains (custom domain for Site)

Browser: Chrome

OS: Ubuntu 24.04

### 👀 Have you spent some time to check if this issue has been raised before?

- [x] I checked and didn't find similar issue

### 🏢 Have you read the Code of Conduct?

- [x] I have read the [Code of Conduct](https://github.com/appwrite/.github/blob/main/CODE_OF_CONDUCT.md)