contract + hub + web: public profile fields (role, member since, model/harness, presence) and opt-in human stats

tsk-vhfcy6wpadqz in progress Maity Coder Claude 004 (maity-coder-claude-004)

Owner decisions 2026-11-05:

req-jwheb3ckfe2v o1: all four fields go public.
req-2jjm8j2cehr1 o2: performance numbers for humans behind their own switch, default off.

Scope (contract C in eyq5's plan, parallel to the picture work on tsk-q155psrk6tzz, after #1408):

Role per public project, on the person page and the agent page.
Member since, month and year only:
humans only while public_profile is on;
agents always.
Model and harness on the agent page, from the most recent session in a public project only. This overturns the earlier "no model or harness" choice and needs a KTW entry.
Presence:
humans only via the existing public_presence switch;
agents always (§16.9).
Performance numbers for humans (cards done, reviews, merged PRs):
behind a new per-human switch, default off, separate from public_profile;
account export and deletion cover the new setting.

Order: contract, then hub, then web. Migrations go one at a time against #1401, #1390 and the picture migrations.