feat(vita): add native-density rendering and touch input

[doodlewind]

Summary

• add target-owned raster density while preserving the 480x272 logical viewport; Vita now renders fonts, SVGs, masks, and optional @2x assets directly at 960x544
• expose platform.pixelRatio and make PSP GE, Vita GXM, WASM, capture, and low-level demo builds consume the same resolved density contract
• add first-class immutable front-touch snapshots in logical coordinates, bump the Vita Host ABI to 2, and let DeepZoom consume anchored pan/zoom gestures while PSP keeps controller fallback
• derive stable Vita Title IDs from each manifest app ID and keep named VPK outputs so demos and downstream apps install as separate bubbles
• replace duplicated-pixel Vita assertions with independent native-detail goldens, texture/font residency checks, and touch/input semantic capture hooks
• fix the shared motions grid layout
• keep the Vita hardware-install guide, but remove the unfinished Vita blog draft from this PR

Validation

• bun run test
• PSP headless golden suite: 44/44 byte-exact
• Vita3K native-density golden suite: 44/44 byte-exact
• focused DeepZoom/touch tests: 7/7
• Rust core tests: 64/64
• native Vita release VPK builds at density 2
• site build with the Vita draft absent

Downstream proofs

• pocket-figma#1: gesture tests 8/8; PSP/Vita platform checks; local and cold Vita3K 7/7; one-finger pan continues with measured post-release inertia; two-finger anchored pinch measures exactly 2x with a fixed document center
• open-strike#9: PSP/Vita platform checks; Vita host tests 10/10; cold right-stick capture changes yaw while centered pitch has zero drift
• stable install IDs remain independent: stock demos derive IDs from manifest identity, Pocket Figma uses PFIG00001, and OpenStrike uses OPSK00001

This follows merged #98 and #92; all three PRs remain draft and this branch is not merged.