v0.39.0

Added

• usb_c_power_in library component. A power-only USB-C sink as a
  subcircuit: the 16-pin USB 2.0 receptacle, a 5.1k Rd pull-down on each
  CC line (without them a C-to-C cable from a compliant source never
  turns VBUS on) and a bulk cap, wired VBUS -> 5 V rail, GND -> GND.
  For designs whose load, a motor bridge or an LED strip, should not run
  through the dev board's own USB port. No ESPHome config of its own.
  Example usbc-led-strip feeds a WS2812B strip from one.
• create_design MCP tool. The design-editing tools needed a design
  that already existed in the store, and nothing on the MCP surface could
  put one there: a client with a finished design.json had to go through
  the web UI or the REST POST /designs behind the browser's SSO.
  create_design takes the document, checks it the way validate does,
  stores it under its id and makes it the active design. An existing id
  is refused unless overwrite is set.
• Flash size override in the Inspector. ESP32 boards get a flash size
  select under the board picker: "Board default (NMB)" or 4/8/16/32 MB,
  writing board.flash_size_mb. Raising it above the board file's value
  shows an inline boot-loop caution, matching the
  flash_size_override_above_board warning (#219).

Fixed

• Switching boards in the web UI drops board.flash_size_mb, as the
  agent's set_board already did. A size measured on one board was being
  carried to the next.