Add serialType field to auto-select CDC vs UART firmware variants

[DTTerastar]

Summary

• Adds an optional serialType: "cdc" | "uart" field to the Build interface in the manifest schema
• Detects whether the connected device uses native USB CDC (Espressif VID 0x303a) or an external USB-to-UART bridge via port.getInfo()
• Automatically selects the matching firmware variant when multiple builds share the same chipFamily

Motivation

Chips like ESP32-S3 and ESP32-C3 can be connected either via their built-in USB CDC port or via an external USB-to-UART bridge. These two connection methods require different firmware builds (different compile flags). Previously, users had to manually choose the correct variant — or the wrong firmware could be flashed silently.

This was originally requested in #383, which was closed with the conclusion that detecting the connection type was not possible. However, port.getInfo() from the Web Serial API does expose the USB vendor and product IDs before any communication begins, making detection straightforward. Espressif's native USB CDC devices are identifiable by VID 0x303a and known CDC product IDs, as noted in the discussion on #383 itself.

The Tasmota approach (single firmware that detects CDC at runtime) is a valid alternative, but is not always available — particularly for projects that need separate binaries for each transport type. This feature is purely additive and requires no changes for projects that don't need it.

Behavior

Build selection priority:

1. Exact match: build with chipFamily + serialType matching the detected connection
2. Generic fallback: build with chipFamily and no serialType specified
3. Not supported: if neither is found, installation is refused — avoiding silently flashing the wrong transport variant

Manifests without serialType are completely unaffected — existing single-variant manifests continue to work as before.

Example manifest

{
  "chipFamily": "ESP32-S3",
  "serialType": "uart",
  "parts": [...]
},
{
  "chipFamily": "ESP32-S3",
  "serialType": "cdc",
  "parts": [...]
}

Closes #383
Related: #331