Add A Beta Deployment Workflow

[Perplex]

ref CSF-1080

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Note

Medium Risk
Automates packaging/publishing of a staging extension build and alters manifest/environment selection based on a new staging mode; main risk is misconfiguration leading to incorrect extension metadata/permissions or unintended publishing to the Web Store.

Overview
Adds a new GitHub Actions workflow (submit_staging_chrome.yml) that builds a staging Chrome extension on master/manual runs, zips it, uploads it as an artifact, attempts to cancel any pending Web Store submission, and then publishes via the Chrome Web Store API using stored OAuth/CWS secrets.

Introduces a build_staging script plus a new environment.staging.ts, and extends webpack.config.js to support a staging mode that swaps in staging environment config, appends the GitHub run number to the extension version, and rewrites manifest metadata/connectability (e.g., adds csfloat.build matches and "STAGING" naming) and version.txt accordingly.

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