Cap loading page progress at BACKFILL_MAX_POSTS; show truncation notice on profile
The loading page denominator now reflects the actual backfill target
(min of profile post count and BACKFILL_MAX_POSTS) instead of the raw
post count, and the progress bar initializes at the current fetched
value on refresh rather than resetting to zero. A persisted `truncated`
flag on backfill_jobs records whether the cap was hit, so the profile
page can show a "posts since <date>" notice independent of the current
env var value. The progress bar is now a rounded div with a smooth
CSS transition instead of the native <progress> element.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>