Add --speed fast/medium/slow profiles for embed operations

Speed profiles control timeout, retries, batch size, and delays:
  fast:   30s timeout, 7 retries, batch 10, 1s delay (~5x faster)
  medium: 60s timeout, 5 retries, batch 5, 2s delay (default)
  slow:   300s timeout, 3 retries, batch 5, 5s delay (safe)

Analysis showed 54% of batches hit 300s timeout on Olla bad routes,
wasting 7.7h on 155 batches. Fast mode reduces timeout waste from
300s to 30s per bad route — real embeds take ~18s on average.

Also reduced default batch delay from 5s to 2s in config.yaml.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

config.yaml

@@ -26,7 +26,7 @@ embedding:
 # Batch processing — avoid API rate limits
 processing:
   batch_size: 50          # files per batch
-  delay_between_batches: 5 # seconds
+  delay_between_batches: 2 # seconds
   max_concurrent: 3       # parallel uploads
   skip_extensions:        # don't process these
     - ".bin"