fix(sdk): use boolean private field and correct repository directory

[overbalance]

Which problem is this PR solving?

The packages/sdk/package.json added in #288 has two metadata mistakes and one inconsistency:

• private is set to the string "true" instead of the boolean true. npm treats any truthy value as private so publishing is still blocked, but the value does not conform to the package.json schema.
• repository.directory points to packages/browser, a directory that does not exist in this repository.
• The exports map lists the root "." entry after the subpath entries.

Short description of the changes

• Change "private": "true" to "private": true. The package is intentionally kept private for now; publishConfig is left in place for when it is ready to publish.
• Change repository.directory from packages/browser to packages/sdk.
• Reorder the exports map so the root "." entry comes first, matching common convention. This is cosmetic; resolution behavior is unchanged.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• npm run validate passes (API compliance, web API baseline, package exports/publint, bundle size, module integrity)
• npm run lint (biome, tsc, eslint) passes via the pre-commit hook

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added (not applicable, metadata-only change)
• Documentation has been updated (not applicable)