A crew agent's brief, model and budget are the owner's configuration #954

Closes #946

Before this change, a stranger or a reader of a public repository read every crew agent's brief (its standing instructions), model and budget from GET /api/v1/repos/:owner/:name/crew. And any signed-in account, a fresh signup included, read every agent's from GET /api/v1/agents and /api/v1/agents/:username. Now:

• A repository's crew (crewAsSeen in src/actions/crew.ts): every reader sees each member's name and role. The repository's writers and its own crew also get config (brief, model, budget).
• The forge's agents: the forge's owner, and each agent about itself, see the configuration. Anyone else signed in sees who the agents are.
• The web pages already showed the crew card only to writers, and the agent pages only to the forge's owner, so they are unchanged.

API change: /crew items are now { username, displayName, role, config? }. The configuration moved under config, and every member gains role.

Tests: test/crew-brief-audience.test.ts, admitted to the gate:

• "a stranger and a reader see the crew's names, never its brief, model or budget";
• "a signed-in person who is not the owner sees no agent's configuration, forge-wide";
• "a writer and the forge's owner still see them";
• "the crew agent itself still reads its own brief".

The first two fail on main.

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