Call them coworkers on the page that creates them

[krongggggg]

What this changes

PR #11 renamed the product noun to coworker and updated the create form, then missed the roster that opens it. Clicking New agent opened a panel titled New coworker.

This changes only the leftover user-facing strings on that flow:

• Roster heading, empty state, explore heading, and the button that opens the form
• Profile helper text that still said "agents list"
• Sidebar empty-state line, plus the nav label next to that copy

Routes, file names, identifiers, /bot, and AG-UI "Bot" are unchanged.

Where it runs

• New state that outlives a request? None.
• What happens on the second replica? Same strings on every replica.
• Anything serialised? None.
• Anything fanned out to a browser? None.
• New listener, port, or schedule? None.

Boundary and audit

• Every acting call still goes through the gateway: resolve, decide, audit, then act.
• New refusals and new failures each write a row.
• Nothing new is trusted from the client that the server can resolve itself.

Proof

Copy-only.

• bun run format:check — clean
• bun run lint — exit 0
• bun run typecheck — app, server, worker all clean
• bun test app/tests — 53 pass, 0 fail

Test plan

• Open /agents and confirm the heading, empty state, and create button say coworker
• Click the create button and confirm the panel title still matches
• Confirm /bot and AG-UI "Bot" copy is unchanged