fix(ecs): harden filter rasters and resource caches with regression coverage

[xiaoiver]

Filtered multiline gradient text could disappear because each line clipped the previous line, and a 50% fill could become 25% opaque. Render-cache keys could also change when callers edited sampler descriptors, while failed LUT uploads leaked the newly allocated texture.

This change builds one complete text mask before clipping, applies text opacity once, and stacks CSS gradients with the first layer on top. Filter rasters now use the configured canvas adapter. Resource caches snapshot sampler descriptors, distinguish the volume-texture W address mode, normalize pipeline/layout keys before lookup without modifying caller-owned input, and release LUT textures on upload failure.

Adds 69 behavioral unit tests and a small Chromium pixel regression for native Path2D, conic gradients, and multiline text. Canvas pixel tests use real Cairo; GPU cache tests use allocation/upload doubles to assert resource identity and ownership. New coverage gates protect the three tested modules. The full ECS source collection remains unchanged.

Coverage	Before	After
ECS lines	63.77%	65.23%
ECS branches	50.57%	51.57%
Filter raster lines	8.55%	91.81%
Render-cache lines	90.32%	100%
Cube-LUT-cache lines	18.33%	100%

Validation:

• Full ECS suite with coverage: 199 suites / 1205 tests passed, all coverage gates passed, about 8m57s in Node 20 with native canvas/headless-gl and Xvfb. The previous batch's two sorting timeouts passed in this full run.
• Chromium filter-raster regression passed. Browser checks are separate from Jest coverage.
• Full repository ESLint, browser TypeScript project, and a targeted TypeScript project for the new unit tests passed.
• New test/config/changeset formatting and git diff --check passed.

Baseline is merged master 00deb2bf. Coverage numbers are from local full-package reports; Coveralls updates after merge and CI. See docs/ecs-test-coverage.md for scope, counts, gates, reproduction commands, and the next atlas/image/batch lifecycle priorities. Includes patch changesets for ECS and device-api; no package publication.