Prepare repo-only Horizon screenshot review candidates

[shiny-code-app]

The approved store images predate Horizon. This prepares 14 repo-only review candidates across Mac, iPhone (both existing display sizes), iPad, Vision Pro, Watch, and Apple TV, with an image index and one checksum/provenance manifest. Refs #744; the approval/upload finish line stays open.

The operator renderer gains an app-store synthetic scenario with readable names and candidate canvases. These are unapproved host-rendered shared-view compositions, with missing app navigation/OS context, isolated Watch content, flat Vision Pro composition, compact clipping/truncation and widget magnification disclosed. Shipping views, installed runtimes and uploader mappings are untouched. No App Store upload or submission occurs.

Validation: commit gate passed Python checks and 1,293 Swift tests. All 14 images reproduce byte for byte from final renderer source; dimensions/checksums and opaque pixels verified, and images visually reviewed. Two Anthropic claude-opus-5-5 review passes; findings and final corrections recorded in discussion. JetBrains UNKNOWN / scope_semantic_coverage_missing (configured PyCharm lacks Swift support). CI is running green-so-far; Supervisor rechecks before queueing.

There is no product behavior for a Client to test in this preparatory PR. Chris's image approval remains on #744.

[shiny-code-app]

Ready for the merge train

Head: 25e8f1e

[shiny-code-app]

CP-744-D1 review and evidence for head 25e8f1e:

Anthropic claude-opus-5-5 reviewed the preparation and first corrections in two read-only passes (7fccc32 and d5e907a); neither reported a blocking issue. Final corrections: surface-matched padding and opaque widget backgrounds; scenario lookup tied to --scenario; clipped iPhone content and widget magnification disclosed; exact hash input named; invalid scales rejected; real PNG byte/dimension tests added; padded render paths covered. All 14 images reproduce byte for byte from final renderer source and have opaque pixels. A Swift-source hash assertion was declined under the repo's source-text test ban; the exact digest was independently recomputed. Contrived flag-as-argument ambiguity and the unused app-store/reset-deadlines combination remain inherited limitations outside the manifest's supported invocations.

Final commit gate passed Python checks and 1,293 Swift tests. JetBrains UNKNOWN / scope_semantic_coverage_missing: configured PyCharm lacks Swift semantics. No clean IDE result claimed. Links, dimensions, hashes and visual assets checked. No app/extension bundle was built or installed.

CI registered for this head and was running with zero observed failures at handoff. The strict ready helper refused pending checks without writing. Q177/CP-744-D1 permits green-so-far handoff, so the separate ready comment uses the exact SHA format; the Supervisor watcher rechecks before queueing. No label or merge applied.

The PR stores unapproved shared-view compositions only. #744 stays open for Chris's image approval and any required complete app/OS-composited captures. No uploader mapping, App Store version, upload or submission changed. Follow-ups stay in this handoff; no new issue. Existing repository merge prose contradicts current overall direction/brief; routing follows the train, and this screenshot task did not change execution guidance.