[P3] rental-housekeeping-overlay-blank: rentals get no cleanliness cell, reading like an unreachable hotel room

Deferred from the /gds-code-review Acceptance Auditor on PR #633 (Modern rental living, v2.0.0).

src/engine/sim/congestion.ts:276 gives u.kind === "condo" an explicit tint: "na" cell, with a comment recording exactly why: "a blank condo reads exactly like an uncovered hotel room". That is a deliberate fix for a real ambiguity in the housekeeping overlay.

The two new residential kinds are labor-free by design (GDD §7, D9) but get no cell at all, so a Studio or Apartment floor on the cleanliness map is indistinguishable from a hotel room no housekeeping crew can reach. This is the same ambiguity the condo "na" tint exists to prevent, reintroduced for the new kinds.

The occupancy and satisfaction overlays are fine: they are kind-generic (FACILITIES[u.kind].population > 0).

Fix when picked up: give both rental kinds the same tint: "na" treatment as the condo.

/gds-code-review.

Start in src/engine/sim/congestion.ts at line 276 and read the existing condo tint handling and its rationale. Apply the same tint: "na" treatment to the two rental kinds, then verify that Studio and Apartment cells are no longer blank on the cleanliness overlay while occupancy and satisfaction overlays remain unchanged.