Clear every compiler warning in our own sources (Swift 6 groundwork), and fix the blur relay's fake weak capture

[straff2002]

Clears every compiler warning in our own sources (app + test targets). Several were "this is an error in the Swift 6 language mode", so this is also Swift 6 migration groundwork. Vendored/SPM warnings are out of scope.

One real bug

OutboundFrameRelay.blur — the inner queue.async sat inside a closure that had already bound self strongly via guard let self, so its [weak self] Task was decorative. A relay released mid-pipeline was held alive to finish the composite and publish one more frame. The outer capture is weak now, which is what the surrounding code always intended.

Main-actor isolation

Immutable configuration made genuinely nonisolated rather than hopping — these are read from CoreBluetooth and capture callbacks where an actor hop would change timing.

• EvenBLETransport's characteristic UUIDs and advertised-name prefix. CBUUID isn't annotated Sendable, so the three UUIDs are nonisolated(unsafe) — immutable value objects created once, stated rather than worked around.
• LocalLLMService.visionModelIds, LLMService.localSafeTools, VideoRecordingService.frameStallSeconds.
• FingerspellingModelDownloader.liveInstaller moves onto the nonisolated FingerspellingModelBundle, mirroring the existing ASRModelBundle precedent. That also resolves the redundant await progress(...): the closure is no longer main-actor-inferred, so the hop is real — and the download's file I/O leaves the main thread.

Sendable

• The vision turn's UserInput (and the CIImage in it) is built inside the @Sendable closure from Sendable ingredients only, instead of crossing the boundary.
• MediaTriggerService's notification handler is typed @Sendable.
• BroadcastAudioProviding is @MainActor — the adopter and both call sites already were; only the handlers it registers are @Sendable.

iOS 26 deprecations

Deployment target is 26.0, so no availability gates were needed.

• The OAuth presentation anchor walks connected scenes: foreground-active key window → any key window → any window → a new window on a scene. init(windowScene:) is the only surviving UIWindow initialiser, so the scene-less tail traps rather than returning an unpresentable empty window. Worth a reviewer's eye — it's a new trap where there wasn't one, though signIn() is only reachable from a Settings button tap, which requires a live scene, and the empty window it replaced could never have presented anything.
• Walking routes use MKMapItem(location:address:) instead of the deprecated MKPlacemark.

Also

Two discarded capturePhoto() results made explicit (it files every capture to the "Glasses" album itself), a discarded seekToEnd(), two redundant trys on non-throwing closures passed to a rethrows function, and three redundant awaits in the download tests.

Verification

• Debug simulator build: clean, 2852 tests, 0 failures, 3 skipped
• Release build (device arm64, real SDK): succeeded, zero warnings in our sources
• Debug device build: clean, installed and running on hardware

Every edited file was confirmed present in the build's SwiftCompile lines — an incremental build can silently skip a file, making a fixed warning and an unrecompiled file look identical. Three fixes initially looked verified and weren't; they were forced to rebuild and re-checked.

Build bumped to 351 per the per-merge convention; marketing version unchanged (no new feature).

Not addressed

Two xcodebuild notices remain, both pre-existing and neither a compiler warning: OpenGlasses/Sources/Models and .../Shared are members of multiple groups in the generated project. That's a project.base.yml group-layout artifact from the widget target referencing individual files inside a directory the app target includes wholesale — changing shared-file group placement risks the widget's target membership, so it's left alone.

Separately, a Release build does not launch on device — see #304. That's a vendored-dependency static-init deadlock, unrelated to this PR (the Release compile here is clean; the hang is pre-main).

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