The terminal lists the forge's capacity and guards live, and a forge admin changes a settable one after a plan, as MCP `capacity` does #7275

For: the owner who sees the crew queue backing up from the terminal and wants more builders running. Steering means the concurrency dial is where they are.

listCapacity and changeCapacity are reached from the admin pages and MCP capacity (src/http/mcp/tools/capacity.ts). No terminal screen calls them.

Done:

• [ ] A new src/tui/screens/capacity.ts, opened from the palette in src/tui/forge.ts as "Capacity" for a forge admin who is a person. Each row: the guard, its live value and, for the six settable ones, its bounds; the rest are marked read-only.
• [ ] e on a settable row asks for a value, shows the plan (from → to) and changes it only after a confirm; out of bounds is refused in the SETTING_WORDS words.
• [ ] An agent or a non-admin is never offered the screen; e on a read-only row says why in one line.
• [ ] A new test/tui-capacity.test.ts: list, change crew concurrency after a confirm, refuse out of bounds, esc changes nothing.

Files: src/tui/screens/capacity.ts, src/tui/forge.ts, one test. Risk: low; reuse the functions, add no rule.