fix: Various improvements to WHEP input, AES67 output, and logging

[srperens]

Summary

• WHEP Input: Add capsfilter (48kHz) after liveadder, expose mixer_latency_ms property (default 30ms)
• AES67 Output: Set processing-deadline on udpsink to match ptime value
• Logging: Move verbose stats/latency/WebRTC logs to trace level
• Frontend: Fix WASM "env" module error by enabling wasm-bindgen feature for instant crate

Changes

WHEP Input block

• Added capsfilter after liveadder to enforce 48kHz sample rate for downstream compatibility
• Exposed mixer_latency_ms property (default 30ms instead of 200ms) for lower latency
• Fixed liveadder latency property type (expects u32 milliseconds, not ClockTime)

AES67 Output block

• Set processing-deadline on udpsink to match the ptime value for proper packet timing

Logging improvements

• Changed verbose stats, latency query, and WebRTC stats logs from info! to trace!
• Reduces log spam during normal operation while keeping debug info available

Frontend WASM fix

• Added wasm-bindgen feature to instant crate for WASM builds
• Fixes "Failed to resolve module specifier 'env'" error in browser console

Test plan

• Start backend and verify web UI loads without console errors
• Test WHEP input with audio stream
• Verify AES67 output timing
• Check that logs are less verbose at info level

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