release: ship Mirage imagery and ScoreKit 0.7 support

[jamiesun]

What changed

• adds the Mirage music-reactive cinematic particle imagery, deterministic
  showcase, registry wiring, tests, and reviewed bundle budget
• adds a 72,000-sample orbital band, rotating procedural planet, moving
  blue-violet streams, twinkling stars, steel-blue terrain, restrained ship
  dynamics, volumetric exhaust, parallax dust, and beat-driven pulses
• fixes ring/planet compositing, permanent shockwave halos, jagged planet
  edges, sparse exhaust, and competing color families
• moves the application contract to ScoreKit 0.7 with exact clips,
  deterministic automation, renderer-profile certification, richer
  observation, and strict orchestration schema validation
• refreshes v0.3.4 release notes

Why

Mirage gives scorebench a second focused single-world imagery with a cinematic,
music-driven scene while preserving the observation-only WebAudio/Three.js
boundary. The ScoreKit 0.7 work keeps the workbench aligned with the compiler's
current machine-readable contract.

User impact

Users gain a new fullscreen/recordable imagery with clearer depth, continuous
motion, and music-reactive dynamics, plus first-class ScoreKit 0.7 scene
support. No audio rendering or network responsibility moves into the frontend.

Root causes addressed

• additive planet, atmosphere, shockwave, and ring layers were visually
  compounding
• repeated beats could continuously reset the planet wave
• particle skin extended into the silhouette and post-processing targets lacked
  multisample edge smoothing
• the original exhaust used too few, too-small particles with a narrow authored
  spread
• orchestration schema drift was not rejected early enough

Verification

• npm run check
• npm test -- --run — 14 files / 164 tests
• npm run build
• npm run check:bundle — Mirage 33.1 KiB raw / 10.5 KiB gzip
• cargo fmt --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test — 179 unit tests + 1 Tauri boundary test
• actionlint .github/workflows/*.yml
• mdbook build docs-site
• GITHUB_REF_NAME=v0.3.4 node scripts/check-tag-version.mjs

All checks above were rerun from a detached clean worktree at the proposed
release commit.