feat(config): let the consuming app supply the default project config

[gmaclennan]

What

Stop bundling @comapeo/default-categories in this module. The consuming app now supplies the default project config (presets/categories) via the Expo plugin, so it decides what new projects start with. Passing no config (undefined) is valid — new projects then start empty.

Closes the goal of not shipping a baked-in default config from this module.

How

The config travels app → native → backend:

1. Plugin (app.plugin.js) — new defaultConfig prop (path to a .comapeocat, resolved relative to the app project root, fails prebuild loudly if missing). At expo prebuild it copies the file to a fixed on-device name comapeo-default-config.comapeocat:
   • Android → app/src/main/assets/nodejs-project/ (rides the existing asset→filesDir extraction).
   • iOS → app bundle + registered in the Xcode Resources build phase.
2. Native readers resolve the bundled file to a real filesystem path and forward it to the backend as a new 4th argv positional (after privateStorageDir, before the --sentry* flags). Empty string when none, so a sentry flag can't slip into the slot.
   • Android: NodeJSService.kt checks the extracted file in nodeProjectDir.
   • iOS: NodeJSService.swift uses an injected resolveDefaultConfigPath closure backed by Bundle.main.
3. Backend (backend/index.js) reads the positional (empty → undefined) and passes it through createComapeo to MapeoManager (which already types defaultConfigPath as optional).

Also removed @comapeo/default-categories from backend/package.json, the lockfile, and STATIC_ASSET_PATHS in rollup.config.ts.

Verification

• expo prebuild on the example app with defaultConfig set: confirmed the file lands in Android assets/nodejs-project/ and in the iOS bundle + Xcode Resources build phase.
• Cleanup path: removing the prop deletes the copied files; dropping the iOS Xcode reference requires expo prebuild --clean (documented in the README — xcode's removeResourceFile throws on RN/Expo projects that lack a Resources PBXGroup, so we don't hand-roll pbxproj surgery).
• Argv positional contract verified on both platforms; backend/loader.mjs's strict parseArgs is unaffected (positional, not a flag).
• A multi-agent code review found no blockers.

Notes for reviewers

• New-project behavior changes for apps that don't set defaultConfig (incl. the example/e2e app): projects now start with no presets/categories. The e2e tests create their own fixtures and don't depend on the default config.
• The committed nodejs-project asset trees still physically contain the old bundled file until the backend is rebuilt — it's git-ignored build output and won't ship; rebuild the backend before release so the trees match the new rollup config.

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