fix(ld-svelte-example): fix build if no .env is specified

[joker23]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Describe the solution you've provided

• Made the svelte example build not depend on the creation of a .env file
• This should fix running yarn build on monorepo root
• Added svelte example app build to CI to ensure this doesn't happen again

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Note

Low Risk
Small changes limited to the example app’s env var handling and an added CI build step; no production SDK logic or security-sensitive code is modified.

Overview
The Svelte example now defaults public env variables so it can build without a .env file (imports $env/static/public as an object and provides fallbacks for PUBLIC_LD_CLIENT_ID and PUBLIC_LD_FLAG_KEY).

CI for sdk/svelte now builds the example workspace (ld-svelte-example) as part of the GitHub Actions workflow to catch future build regressions.

^{Written by Cursor Bugbot for commit a2d1f0e. This will update automatically on new commits. Configure here.}

[github-actions]

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 25394 bytes
Compressed size limit: 26000
Uncompressed size: 124693 bytes

[github-actions]

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 18984 bytes
Compressed size limit: 20000
Uncompressed size: 98086 bytes

[github-actions]

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 23334 bytes
Compressed size limit: 25000
Uncompressed size: 81070 bytes

[github-actions]

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 171382 bytes
Compressed size limit: 200000
Uncompressed size: 798175 bytes