Add Brave iOS User Agent Type Study

[StephenHeaps]

Intentional draft PR while testing

[github-actions]

✅ Test Seed Generated Successfully

To apply the test seed:

1. Desktop: Launch the browser with --variations-pr=1617.
   Android: Set the command line to --variations-pr=1617 in debug menu, restart the browser.
   iOS: Set Variations PR to 1617 in Brave Core Switches debug menu, restart the browser.
2. Wait 5-10 seconds to fetch the seed.
3. Restart the browser to apply the seed.
4. Ensure Active Variations section at brave://version starts with the expected seed version (see below).

Seed Details

Parameter	Value
Version	pull/1617@6d4420f6f7c78696a49eac50502997b3b3cf39ad
Uploaded	Fri, 13 Feb 2026 18:42:59 GMT
PR commit	08602a1
Base commit	e9a5f76
Merge commit	6d4420f
Serial number	dfcc1981dbbf16260e38bebf2667a52b