[ryanbr]

Post-merge parity fix for #1584 (@pipiche38's #1568). Found while re-reviewing the merged state.

The divergence

The Oura SpO2 candidate branch resolved "is this owner an Oura device" differently on each platform:

Kotlin   DeviceBrandCatalog.isOura(owner)                        -> device-id PREFIX
Swift    regDevices.first { $0.id == owner }?.brand == "Oura"    -> registry BRAND string

Not stylistic. The two keys can disagree, and when they do it is an analytics split: a device with
an oura- id but no registry row — or a row whose brand text differs — was Oura on Android and not on
iOS, so Android computed the ceiling@100 candidate for that night and iOS did not. That is precisely
what the parity contract forbids.

A byte-identical Swift twin already existed:

public static func isOura(_ deviceId: String) -> Bool {
    all.first { deviceId.hasPrefix($0.idPrefix + "-") }?.sourceKind == .oura
}

Repository.activeDeviceIsOura already uses it, with a comment saying it is there "rather than an
ad-hoc 'oura' literal". Swift now uses it too.

The id-prefix key is also the safer one

Not just more consistent — more robust. Repository.swift:178 records that the registry mints every
non-WHOOP id as "<idPrefix>-<uuid>", so the prefix IS the brand key and is always present, while
the brand compare needs a registry row to exist and its text to match.

I verified Oura ids really are minted that way before changing anything —
SourceCoordinator.swift:453 builds "\(ExperimentalBrand.oura.idPrefix)-\(serial)" → "oura-<serial>"
— because if they weren't, this "fix" would have silently disabled the Oura path it exists to protect.

WHOOP owners are unaffected: my-whoop and my-whoop-noop fail the prefix test exactly as they failed
the brand test, so they still take the v18 aux branch.

Checked and deliberately left alone

skinTempWornToleranceSec keys on the brand string on both platforms (Swift :2363, Kotlin :77),
so that pair is symmetric — a different convention from the catalog, but not a divergence. It predates
#1568 (from #1467) and is out of scope here.

Verification

• Kotlin untouched — it already used the catalog.
• doc_comment_lint.py clean. No strings, no schema, no behaviour change for WHOOP owners.
• app-build required — app-target Swift, nothing else compiles it. Not dispatched.
• Not seen on a device. Neither was the original: @pipiche38's device capture with the toggle flipped
  on is still owed, and it now also exercises this resolver.