[Beta.2 continuous cleanup] Externalize immutable media and reduce repository weight

[SisyphusZheng]

Scheduling amendment: ADR-0152 / #1341. Active lane: Beta.2 continuous cleanup; scope below is retained except superseded train timing. No implementation completion is claimed.

Current scope

Continuous cleanup under #1322 begins during Beta.2.1; no waiting for a former Beta.3 lane. Preserve distinct residual obligations and do not duplicate #1328-#1334/#1156. RC-only qualification remains a later gate.

Part of #1155 and #1192. Target: 1.0.0-alpha.x.

Objective

After website architecture stabilizes, externalize immutable production media and reduce source-tree fixtures, visual baselines, and design assets.

Scope

• content-addressed CDN/object-storage media
• provider-neutral asset manifest and integrity verification
• design-original cleanup
• minimal deterministic offline fixtures
• visual-baseline artifact/bundle policy
• repository-size reduction without rewriting Git history

Boundary

This issue does not block compiled Alpha architecture unless a specific asset prevents a required test. Core compiler/runtime tests must not depend on CDN availability.

Acceptance

• Production media integrity is deterministic.
• Source-tree media and fixture ownership is intentional and materially smaller.
• No destructive history rewrite occurs without separate explicit approval.

[SisyphusZheng]

Reconciled into the NEW release train (umbrella #1155, baseline 2936bf0). The old Alpha.1–8 / five-Beta topology is obsolete; supported topology: A10 → B1 → B2 → B3 → RC1 → Stable. This issue is reused (not duplicated) — see the umbrella child-issue checklist for its exact mapping.

Kept as a Beta.2 related issue (repository weight / asset externalization supports productization). Not a Beta.1 blocker.

[SisyphusZheng]

Phase-0 reconciliation (Beta.2 stage #1288): moved to the Beta.3 milestone. The title already targets beta.3; it was misfiled in Beta.2.