[JakubMrozek]

Summary

Restores per-session AVAudioSession activation for OMID video sessions, fixing a regression where hardware device-volume changes were not delivered to the IAB OMID verification script.

What changed

OMManager.createSession, for creativeType == .video, now inlines:

```swift
let session = AVAudioSession.sharedInstance()
try? session.setCategory(.playback, mode: .default, options: [.mixWithOthers])
try? session.setActive(true)
```

…called per video OMID session, immediately before the OMID context is created. Matches the IAB OMSDK demo's WebViewVideoController.swift and the sdk-swift v3 PR #119 pattern that was IAB-certified.

Why this is necessary

Prior to this release, OMManager.createSession routed through AudioInfoProvider.ensureSessionActive() — a one-shot lazy static. First access typically came from AudioInfoProvider.collect() during the very first /preload (long before any video ad). By the time a video OMID session started, the static had already evaluated and ensureSessionActive() was a no-op.

That broke OMID's internal outputVolume KVO observer in practice: even with .mixWithOthers, the WKWebView's video element appears to take over audio focus, and iOS stops publishing volume KVO events to observers that registered before the video session was active. Re-issuing setActive(true) per-session refreshes the publishing pipeline.

Hand-verified against the IAB Validator Proxy: with the new pattern, volumeChange events now carry updated deviceVolume values on every hardware volume press (verified deviceVolume: 0 → 0.05 → 0.15 → 0.20 → 0.15 → 0.20 → 0.30 → 0.40 → 0.45 → 0.40 → 0.30 → 0.40 → 0.45 across two test sessions).

What was NOT changed

The "never deactivate" decision stays. setActive(false, .notifyOthersOnDeactivation) is what produced the 1-second audio-cut bug fixed in sdk-flutter PR #51, and .mixWithOthers makes a permanent active session gentle on host audio. The new code only ever calls setActive(true) — never setActive(false).

The earlier AudioInfoProvider.ensureSessionActive() lazy static remains in place for /preload's getDevice() consumer (which uses it to keep outputVolume live for device-info collection); it's just no longer relied on for OMID's per-session KVO.

Test plan

• xcodebuild clean test -scheme KontextKit -destination 'platform=iOS Simulator,name=iPhone 16 Pro,OS=latest,arch=arm64' -skipPackagePluginValidation — green
• Hand-test against sdk-swift Example (Package.swift pinned to local path): play a video ad, press hardware volume up/down, verify volumeChange events with updated deviceVolume arrive at the IAB Validator Proxy
• pod lib lint KontextKit.podspec --allow-warnings --use-libraries
• After merge: tag 0.0.4, GitHub release, pod trunk push KontextKit.podspec --allow-warnings --use-libraries

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