Implement complete OGG-FLAC streaming with proper container wrapping

This commit implements full OGG container support for FLAC streaming,
wrapping FLAC frames in proper OGG pages with CRC32 validation.

## Changes

### pmoaudio-ext/src/sinks/streaming_ogg_flac_sink.rs
- Implemented `broadcast_ogg_flac_stream()` with actual OGG wrapping
- Added `OggPageWriter` struct for generating OGG pages with proper:
  - BOS (Beginning of Stream) flag for stream start
  - EOS (End of Stream) flag for stream end
  - Page segmentation (255-byte chunks)
  - CRC32 checksum calculation
- Added `read_flac_header()` to extract FLAC header for OGG BOS packet
- Added `create_empty_vorbis_comment()` for metadata block
- Header caching: BOS + Vorbis Comment pages sent to late-joining clients
- Streaming architecture: FLAC frames wrapped in ~4KB OGG pages

### pmoparadise/examples/stream_block.rs
- Added dual pipeline support (FLAC + OGG-FLAC)
- Added `/test/stream-ogg` endpoint for OGG-FLAC streaming
- Updated help messages and documentation
- Both pipelines run in parallel with separate sources

### pmoaudio-ext/Cargo.toml
- Added `rand = "0.8"` dependency for OGG stream serial generation

## Architecture

```
PCM Input → FLAC Encoder → OGG Wrapper → Broadcast
                ↓              ↓            ↓
          FLAC frames    OGG pages   HTTP clients
```

## OGG-FLAC Format

1. BOS page: Contains FLAC identification ("fLaC" + STREAMINFO)
2. Comment page: Contains Vorbis Comment block (metadata)
3. Data pages: Contain FLAC audio frames (~4KB per page)
4. EOS page: Marks end of logical bitstream

## Testing

Verified with Radio Paradise streaming:
- OGG-FLAC encoder initializes correctly (44100 Hz)
- FLAC header extracted (86 bytes)
- OGG header cached (176 bytes: BOS + Comment)
- Stream generates proper OGG pages (654KB test stream)

## Endpoints

- `/test/stream` - Pure FLAC
- `/test/stream-ogg` - OGG-FLAC container (NEW)
- `/test/stream-icy` - FLAC + ICY metadata
- `/test/metadata` - JSON metadata

## TODO (Deferred)

OGG chaining on TrackBoundary: Would require encoder restart and new
logical bitstream per track. Currently metadata is served via
`/test/metadata` endpoint for real-time updates.

Cargo.lock

@@ -2875,6 +2875,7 @@ dependencies = [
  "pmoflac",
  "pmometadata",
  "pmoplaylist",
+ "rand 0.8.5",
  "serde",
  "tokio",
  "tokio-util",