* Deploy the web beta to Cloudflare Pages

Pushes to icarus-cloud that touch the web build, and manual runs, build
Flutter web with CI's exact command and upload it to the icarus-web Pages
project as its production deployment (beta.icarusstrats.com). _redirects
serves index.html for share links and the auth callback; _headers makes
browsers revalidate Flutter's unhashed entry files.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* Rely on Pages' SPA fallback and use wrangler-action v4

Pages ignores `/* /index.html 200` as a redirect loop and already serves
index.html for unknown paths when the build has no 404.html, so drop
web/_redirects and document that dependency. wrangler-action v4 installs
Wrangler 4 by default; the job summary now shows the Pages environment so
a run confirms it landed as production.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* Use the assigned icarus-web-a50.pages.dev host in the web deploy docs

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* Deploy the web beta when shaders or path packages change

pubspec.yaml bundles shaders/ and compiles the packages/ and third_party/convex_flutter path dependencies into the web build, so a change to any of them alone must redeploy.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

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Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>