Sprint 15.2 — Add the image metadata adapter and view model

[maruson08]

Problem / motivation

Vendor-native metadata structures and errors must not leak throughout the UI.

Scope

Add the sole vendor import adapter and deterministic DOM-free view model for summaries, coverage states, grouped entries, bounded values, diagnostics, cleaning evidence, and verification evidence.

Non-goals

No generic recursive renderer, guessed schema, pixel decoding, Canvas, or locally duplicated cleaning policy.

Acceptance criteria

• Only metadata.js imports the vendor artifact.
• Adapter admits signature-validated JPEG/PNG/WebP under the 50 MiB app limit and normalizes stable errors.
• Model preserves opaque versus decoded values, duplicate/unknown entries, exact rationals, partial-success semantics, and bounded display values.
• Unit tests cover malformed/partial states and category mapping.

[maruson08]

Completed by PR #29, merged into the v2 integration branch at 82f09e8. GitHub did not apply the closing keyword automatically because v2 is not the repository default branch.