Maintenance board: each worker's findings, actions and their effect, on forge/boards and a home tile #7561

Part of the epic #7553. Last child: blocked by the pipeline model (#7562), the framework (#7554) and every worker (#7555 to #7560).

Problem

The owner likes the bottleneck chart and the boards. The maintenance work needs the same surface so a person can see, without asking anyone, what the workers found, what they did and whether it helped.

Build

• A board in forge/boards (JSON, same file form as other boards; see src/boards/store.ts:2, src/boards/starting.ts) named "Maintenance", created by the forge if missing.
• Top row: the bottleneck stage and the pipeline numbers from #7562 (throughput, wait p95, failure reasons).
• One lane per duty (batch doctor, flow keeper, release keeper, efficiency, performance, rules): last run and result, runs today, findings, actions, spend against budget, a pause switch.
• A findings list from maintenance_run: what was found, the probe and its number, the action, and the link to the issue or pull.
• Effect: each action is followed by the same probe later; the board shows "fixed", "still there" or "worse" (for example npm bytes per hour after #7541, home p95 after #7494, red-batch share after a doctor hold).
• A maintenance_run source in src/boards/sources.ts (no free-text columns that carry user content; probes are numbers and fixed names).
• One home KPI tile: "maintenance: N findings open, M fixed this week", opening the board.

Done when

• The board exists on a fresh forge, renders with no runs ("nothing to do yet") and with seeded runs from every duty.
• Pausing a duty from the board stops its next run and shows paused.
• The "effect" column goes from "still there" to "fixed" when the probe passes in a seeded replay.
• Tests: test/maintain-board-shape.test.ts, test/maintain-board-empty.test.ts, test/maintain-board-pause.test.ts, test/maintain-board-effect.test.ts, test/maintain-home-tile.test.ts.

Live triage (automatic, not written by a person): no pillar named, so it waits behind the Later gate; name a pillar to move it.