Add firmware version picker to web flasher

Lets users choose between the latest dev build and tagged GitHub releases.
The dropdown queries the GitHub Releases API on page load and swaps
firmware fetch paths between Pages-relative and release-asset URLs.
CI now attaches all 4 firmware files to releases (bootloader, partitions,
boot_app0, firmware) so full installs work from any release version.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/release-firmware.yml

@@ -102,6 +102,9 @@ jobs:
           tag_name: ${{ steps.version.outputs.VERSION }}
           name: ${{ steps.version.outputs.VERSION }}
           files: |
+            docs/flasher/firmware/bootloader.bin
+            docs/flasher/firmware/partitions.bin
+            docs/flasher/firmware/boot_app0.bin
             docs/flasher/firmware/firmware.bin
           generate_release_notes: true
           draft: true