fix(DiscoveryMountain): playback progress and stack overflow
- fix pos_sec integer division bug: samples/hz always 0 -> use total_decoded_samples/hz
- increase dm_play stack 12288->16384, dm_fetch 16384 to avoid overflow on 91KB JSON
- allocate mp3dec_t from PSRAM not stack
- add ID3v2 skip for mp3 files with XMP metadata
- reset last_pct on select/start to show progress bar
- remove auto-play for stability, user presses Play manually
- download now uses PSRAM 8192/4096 buffers, simple HTTP/1.0 non-chunked streaming
Tested on 192.168.68.132: fetch 37/232, download 4.3MB ok, playback opens stream sr=16000 ch=1 ok, no immediate crash.
Fixes #autoplay progress issue
Adolfo
343da892bc