refactor(effects-manager): extract GLSL shaders to .glsl files via raw-loader (#886)

[deveshbervar]

Summary

Phase 2 (PR 2a of 2) of the refactoring proposed in #886.

Extracts the two inline GLSL shader strings from effects-manager.ts into dedicated .glsl files,
loaded at build time via raw-loader.

What changed

New files:

• shaders/hover-vertex.glsl — vertex shader extracted from TS string
• shaders/hover-fragment.glsl — fragment shader extracted from TS string
• src/glsl.d.ts — TypeScript declaration for .glsl imports
• src/tests/helpers/glsl-mock.js — Jest mock for .glsl files

Modified files:

• configs/webpack.conf.js — added raw-loader rule for .glsl
• configs/jest.conf.js — added moduleNameMapper for .glsl in tests
• effects-manager.ts — replaced inline strings with ES6 imports
• package.json — added raw-loader as devDependency

Why

From #886 Gap 1: GLSL embedded as TypeScript strings has no validation path — a syntax error only surfaces at WebGL
runtime, never in yarn test:ci.

This extraction is the prerequisite for PR 2b which adds glslangValidator CI validation.

Scope

• Zero behavior change — shaders are identical
• All 25 effects-manager tests pass
• Part of refactor: EffectsManager missing state model, hover color not configurable, no experiment override API #886 — Phase 2, PR 2a of 2