Feature: Add an entry point for manually downloading the corresponding firmware

[laride]

Description

Add an entry point for manually downloading the corresponding firmware.

Due to browser compatibility and other environmental factors, we cannot guarantee that Launchpad will work as expected for every user. Some users already have Flash Download Tool installed or are familiar with esptool, and may prefer to manually download and flash the firmware as an alternative.

Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.

[Copilot]

Pull request overview

Adds a UI entry point that lets users manually download the currently selected firmware binary (as an alternative to web flashing) to improve usability for unsupported browsers/environments.

Changes:

• Adds a “Download Firmware File” trigger and a Bootstrap modal with links to manual flashing docs and a download button.
• Adds updateFirmwareDownloadLink() to keep the download URL in sync with chipset/devkit/framework/device selection.
• Adds CSS styling for the new trigger container.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
js/index.js	Computes and updates the firmware download URL and toggles the download entry visibility based on selection.
index.html	Adds the download trigger UI and modal (including the download button).
css/custom.css	Styles the new download trigger container to match existing UI spacing.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Suppressed comments (1)

css/custom.css:338

• The new .firmware-download-trigger-container rule duplicates the existing .app-info-trigger-container styling, which makes future layout tweaks easy to miss/inconsistently apply. Consider combining them into a single shared rule.

.firmware-download-trigger-container {
    padding-top: 14px;
    margin-left: 18px;
}