make BrowserCode embeddable

[rijulshrestha]

Adds /embed that composes the IDE or a CLI agent from the query string.

<iframe src="https://browsercode.io/embed?repo=github.com/user/repo&view=preview"
        allow="cross-origin-isolated"></iframe>

• agent / repo / framework picks what boots, view picks the panes.
• Adds a crossOriginIsolated check, so a host page missing the headers gets a clear message instead of an opaque boot failure.

Embedders must send COOP: same-origin and COEP: require-corp on their own page.

[cloudflare-workers-and-pages]

Deploying browsercode with    Cloudflare Pages

Latest commit:	0f4d6e3
Status:	✅  Deploy successful!
Preview URL:	https://ef1d7a35.browsercode.pages.dev
Branch Preview URL:	https://embed-options.browsercode.pages.dev

View logs

[rijulshrestha]

@GabrielaReyna I've created a separate docs folder containing some instructions on how to embed for now. Should we have this here in the repo, or just have it in the browserpod docs?

[GabrielaReyna]

Hi Rijul,

Thanks for working on this. I tested the embeddable components and they look great!

• Please address the opaque failure for agents when the headers are not set
• About your question on the documentation, please display it on the read me, or add a link to the md file from the readme. We will have a dedicated doc content in BrowserCode but this should do for this PR.
• On the message when the headers are not set, please add a link to "Learn more" that points to this repo.
• The 'Nothing to boot" message text is overflowing, please adjust it.

[GabrielaReyna]

podBlocker() is not being imported in AgentShell as you do in IdeShell. Hence if the headers are not set correctly in the host site and an agent is embedded, it won't throw the intended message and the failure is opaque. Please correct this.