Profile editor: support age-based content-rating ceilings

[Quick104]

Server PR Silo-Server/silo-server#1359 changes how profile content-rating ceilings are enforced. They now compare minimum viewer ages, and the web profile editor offers four new ceiling values: 6, 12, 15 and 16. The wire format is unchanged: max_content_rating is still a string.

What needs doing

• Profile picker. CreateProfileView.contentRatings lists only G, PG, PG-13 and R. A profile given 12 or 15 on the web has no matching picker tag, so the editor shows no selection. Add the four age values in the same order as the web (G, 6, PG, 12, PG-13, 15, 16, R). At minimum, keep an unknown current value selected and untouched when the profile is saved.
• Fixtures. Refresh the vendored v2 fixtures with make apiv2-fixtures-sync from the server once fix(access): enforce content-rating ceilings by minimum age silo-server#1359 merges. The ETags in index.json and list_progress_ok.json changed.

No other client change is needed. content_rating on items stays an opaque display string.

AI Disclosure

• Harness: Claude Code, running in T3 Code
• Tool(s): Claude Code, GitHub CLI
• Model(s): claude-opus-5-5
• Involvement: AI-written follow-up for a server change the maintainer directed; not yet reproduced in the app
• Adversarial review: n/a