network-tiers: add the curated, SHA-pinned 'balanced' baseline allowlist data file

[wz-gsa]

Part of the neutral-network-tiers epic (ADR 0002 isolation, PR #299).

Scope

Add the curated balanced baseline egress allowlist as a version-controlled, in-repo data file (e.g. integrations/isolation/network-tiers/balanced.yaml), pinned via the existing full-SHA PATTERNS_KIT_REF mechanism. No runtime fetch.

Seed from ADR-0018's vendored list

quickstart feat/msb-balanced-egress already vendors acq.backends/msb-balanced-hosts.txt — a verbatim mirror of sbx policy inspect local-policy. Seed this baseline from that list (it is the same sbx-balanced set), then curate/justify per-entry. Decide whether the canonical home is here (patterns) with quickstart consuming a pinned ref, or the vendored file stays in quickstart — ADR-0018 anticipates migrating it here.

Requirements

• Curate the initial "useful-but-safe" dev set: package registries (npm, PyPI, etc.), AI/model APIs, common source hosts (github.com family), OS mirrors, cert/CRL endpoints. Keep it MINIMAL — every entry is one we vouch is safe for a prompt-injectable agent to reach.
• Each entry documented with WHY it's on the list (one-line justification) so review + future pruning is auditable.
• Governance: additions require CODEOWNERS + security-skill review. Agents may propose entries but never self-approve.
• Schema/validator for the data file (host charset, optional :port, wildcard rules aligned with the msb translation caveats in ADR-0018: **./*. suffix, crl* intra-label globs broaden on msb).

Human decision required: the actual contents of a federally-shipped default allowlist. This issue seeds a proposed list (from ADR-0018's mirror) for human review, not a self-approved one.

Depends on the schema-vocab issue. AI-assisted (OpenCode). Requires human review.

[mogul]

quickstart feat/msb-balanced-egress already vendors acq.backends/msb-balanced-hosts.txt

...in this PR.