Add Apache 2.0 license and bump version to 0.1.5

[mattapperson]

Summary

• Adds Apache 2.0 license file (LICENSE.md) with proper copyright notice for OpenRouter Inc.
• Adds license field to package.json for proper npm package metadata
• Configures Speakeasy generator to include license in package metadata via additionalPackageJSON
• Bumps version from 0.1.4 to 0.1.5 across all configuration files

Background

This PR re-introduces the Apache 2.0 license after previous attempts (#65, #66) in a cleaner, more maintainable way. The license is now properly integrated into the package metadata through the Speakeasy configuration, ensuring it will be preserved through SDK regenerations.

Changes

• LICENSE.md: Full Apache 2.0 license text with OpenRouter Inc. copyright
• package.json: Added "license": "Apache-2.0" field
• .speakeasy/gen.yaml: Added license to additionalPackageJSON configuration
• Version bumped to 0.1.5 in: jsr.json, package.json, package-lock.json, src/lib/config.ts, and Speakeasy lock files

Test plan

• Verify LICENSE.md contains complete Apache 2.0 license text
• Verify package.json has correct license field
• Verify version is 0.1.5 across all files
• Run build to ensure no breaking changes
• Verify npm package metadata will include license field