docs(roadmap): reframe v0.4.0 demand and repoint dual-mode issue to #149

[jraicr]

Follow-up to the v0.4.0 roadmap placement. Two changes:

1. Reframe the INV-7 demand in the v0.4.0 dual-mode section — the documented real demand is now stated as the maintainer's own external-ingestion workflow (research, dependency review, foreign-PR triage), and the out-of-scope note is generalized to "heavyweight service-mesh machinery." Drops an external-project reference from the public roadmap.
2. Repoint the issue link #147 -> feat(compose): dual-mode network/socket containment — contained-by-default, opt-in DooD #149: the dual-mode tracking issue was recreated (clean body), which burned #147. Updates the table row, status line, provenance, and the link reference so the roadmap points at the live issue.

Docs-only. No code/compose/invariant change. Refs #149.