feat(orchestrate): record per-component seed state and read it on promote

[joshua-temple]

Problem

Per-component promotion writes isolated state, but orchestrate still recorded the built version into the shared flat state.<env>, and promote read its source from there. Two components would overwrite each other's seed, and the independent-promotion scenario had to interleave to avoid it.

Fix (coupled write + read)

• Write: orchestrate records state.components.<name>.<env>. The generated per-component workflow writes it via its inline state edit (generator.go), and the orchestrate CLI serializes through WriteScopedState when a component is selected (orchestrator.go, command.go). An empty component records flat state.<env>, byte-identical.
• Read: the promote source read previously consumed the flat seed orchestrate wrote, so scoping the write alone leaves a component's promote with no source deployments. The promote preflight now reads the component's own seed via ReadComponentState and overlays it (statemerge.go, promote.go, command_preflight.go); single-component reads stay flat.

Result: two components orchestrate to the first environment independently, each keeping its own state, with no interleaving.

Verification

go build ./..., go test ./... (2596 pass), go test -race on orchestrate/promote/config (790 pass), golangci-lint run ./... clean; e2e build+vet clean. Single-component byte-identical baseline gate green (the generator state-edit change does not alter single-component output). Concurrent-orchestrate re-apply preserves an unmodeled sibling verbatim (component_seed_test.go). New scenario 52-component-orchestrate-isolation.yaml (two components orchestrate to dev with no interleaving; both state.components.<name>.dev coexist) passes locally in the harness (30.2s); the promotion-isolation (40.5s) and single-component (55.7s) scenarios also pass locally.

Refs #290, #292.