Profile: a stats section that shows a given profile's numbers

Add a section to the profile page (/app/profile and /app/u/{username}) that shows a handful of stats about that profile.

Background

The old "En chiffres" section was removed. It was video-centric and gave a misleading picture:

• Cumulative watch time and the most active year only counted films and series.
• Top genres were read from the films/series library only.
• The activity heatmap and streak mixed films/series, games and books, but left music out.
• The whole block was gated by the Media domain's Activity visibility facet only.
• It ignored the viewer's enabled domains.

What a new section should do

• One line or tile per domain the viewer keeps enabled, covering every domain (films/series/anime, games, books, music): time spent, items finished, last activity…
• An activity heatmap filtered on the viewer's domains, with music included.
• Per-domain visibility: each domain's numbers follow that domain's own Activity audience, not the Media one.
• A link to /app/stats on your own profile.