feat: add episode progress tracking, resume playback, and last-watched reminder

[v4cachy]

Adds per-episode progress tracking with three features:

1. Visual highlight in episode picker

• Watched/started episodes show a ▶ marker in the episode list (fzf/rofi/dmenu)
• Data stored in $hist_dir/ani-progress (format: id\tep_no\tposition)

2. Position-based resume (mpv)

• Uses mpv's --save-position-on-quit to capture playback position
• Passes --start=<pos> on next play to resume where you left off
• Blocking mode (--no-detach) saves exact position; detached mode saves a watched marker

3. Last-watched reminder

• On startup, shows: You were watching: <title> - episode <ep>
• Reads from existing history file (ani-hsts)

Implementation details:

• New file: $hist_dir/ani-progress
• Modified episodes_list display to cross-reference progress data
• Modified mpv launch to include --start, --save-position-on-quit, and --watch-later-dir
• Post-playback position capture for blocking mode
• Startup message reads last history entry