refactor(workflows): consolidate package commands

[thejustinwalsh]

Summary

• limit contributor-facing manifests to the canonical build, dev, test, and check surface
• move specialized package maintenance into the shared source-metadata workflow index
• make the private external raster proof participate in clean-checkout package checks before benchmark type-checking
• remove rejected MTSDF admission/SIMD runners and redundant command-router self-tests while preserving current oracle, fixture, fuzz, profile, and bake gates
• replace the stale planned-project README with a pre-release v1 workspace landing page, runnable React and Three.js examples, renderer and baking guidance, a concise architecture explainer, and Diátaxis-oriented documentation routes
• correct the font-baker Wasm URL example and route its specialized commands through the workflow index

Verification

• complete root pnpm check passed: Font Baker Rust/public API/integration/fuzz/E2E, Text Rust plus 191 Node and 6 deterministic fuzz tests, 7 external-raster proof tests, 113 benchmark tests, 19 headless product/conformance scenarios, type checks, lint, formatting, package-size evidence, production app build, and documentation
• pnpm bake --help and pnpm scripts show benchmark:presentation executed successfully from the documented command surface
• all 12 local README links resolve
• package source digests matched; OKF v0.2 validation reported 0 conformance errors, 0 producer-profile errors, and 0 warnings

This is PR 3 of 3 and depends on #40.