Add initial Nebula Core packages and docs

Import initial monorepo structure for Nebula Core: add packages (@nebula/core, core-glyphs, core-input, core-navigation, core-theme, core-ui, core-utils) with source, dist, tests and assets. Expand README with overview, quick start and API snippets, and add package-level documentation files. Add jsconfig.json for path mapping, package.json and lockfiles to bootstrap the repo. This commit sets up the project layout, docs, and local package links for further development.

documentation/core-glyphs.md

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+# @nebula/core-glyphs
+
+Controller glyph mappings and lookup helpers. Data-only, no rendering logic.
+
+## What it does
+
+- Maps logical actions to glyph labels per controller type.
+- Provides asset path lookups for common glyphs.
+- Keeps glyph decisions centralized and consistent.
+
+## Included data and helpers
+
+- `glyphMap` — Action-to-label mappings per controller type.
+- `glyphAssetMap` — Action-to-asset-path mappings per controller type.
+- `getGlyph(controller, action)` — Resolve a label.
+- `getGlyphAssetPath(controller, action)` — Resolve an asset path.
+
+## Typical use cases
+
+- Displaying correct prompts for Steam Deck, Xbox, PlayStation, or Switch.
+- Using consistent glyph labels in UI and localization.
+- Swapping controller visuals based on detected device.