fix: surface the requesting scope's own quirk emits into host-aspects spawns

[sini]

Problem

A quirk produced within a user's class context (a homeManager aspect's bare quirk key) does not reach that user's homeManager consumer when the consumer is projected onto the user via den.batteries.host-aspects. The projected consumer sees only host-scope emits (re-emitted host → home), never the user's own — asymmetric with host ↔ nixos, where a host's quirk reaches the host's nixos consumer directly.

Surfaced downstream: an overlay declared on a user-scoped homeManager aspect never reached that user's nixpkgs.overlays, so pkgs.<x> provided by the overlay was undefined in the user's home-manager evaluation. It "worked" only because the aspects carrying such overlays happened to be host-level roles (re-emit covered them); a genuinely user-scoped overlay broke.

Cause

The host-aspects policy.spawn roots the projected consumer with from = the requesting scope's parent = the host scope, and links the spawn root's parent to from. So the consumer's quirk collection walks the host parent chain and never traverses the requesting user scope — its own directly-included quirk emits are outside the walk. #625 added the upward half (surface the spawn's emits up into the requesting scope's imports); the downward half was missing.

Fix

The downward dual of #625.

• spawn-node.nix takes the requesting scope's own raw imports (requestingImports) and merges its non-host-bound quirk emits into the spawn root's imports used for assembly (mergedClassImports) — not into spawnedClassImports, which feeds the upward quirkEmits return (folding them there would double-count the emit back at the requesting scope). Host-bound quirks are excluded (they inherit the host's policy-assembled value, matching the existing strip).
• resolve.nix passes scopedClassImportsRaw.<scopeId> through as requestingImports.
• from = host is untouched, so fix: surface spawn-projected quirk emits at the requesting scope #625's fleet-peer collection is preserved.

Tests

New suite user-class-quirk-exposure:

• test-host-quirk-local-nixos — host ↔ nixos baseline
• test-user-quirk-local-home — user ↔ own home baseline
• test-user-quirk-into-host-aspects-projected-consumer — the repro (failed pre-fix: consumer read [])

Full suite green: 1057/1057.

[sini]

Going to go ahead and merge this fix directly as it builds on #625