Release 1.4.2: load-only dialog when nothing is selected

With neither mode derivable (nothing selected, no marker rectangles,
no config) the dialog now opens anyway instead of failing with an
error figure: both radios disabled with their reasons, OK/Save
disabled, Load config… live - a saved config can bootstrap the run.

README: note that macOS/NixOS field tests last ran with plugin v1.3.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HjSRLWQ8ywBBYyakvr3YTx

README.md

@@ -45,8 +45,8 @@ SWIG API. Requires KiCad **10.0.1+**.
 | Platform                    | Status | Verified by |
 |-----------------------------|:------:|-------------|
 | Windows                     |   ✅   | development platform, full suite before every release |
-| macOS                       |   ✅   | field-tested in KiCad 10 |
-| NixOS                       |   ✅   | field-tested in KiCad 10 ([setup](docs/NIXOS.md)) |
+| macOS                       |   ✅   | field-tested in KiCad 10 (last on plugin v1.3) |
+| NixOS                       |   ✅   | field-tested in KiCad 10 (last on plugin v1.3, [setup](docs/NIXOS.md)) |
 | Debian 12                   |   ✅   | CI test suite in container |
 | Ubuntu 24.04                |   ✅   | CI test suite in container |
 | Fedora (latest)             |   ✅   | CI test suite in container |
@@ -57,16 +57,17 @@ rasterizer, and the platform-fallback regressions — headless against
 the real pip wheels of each Linux row, including the
 `PySide6.QtWidgets` import probe that decides the matplotlib backend.
 What CI *cannot* do is launch KiCad itself, so "runs inside KiCad"
-remains field-tested (Windows continuously, macOS and NixOS per
-release).
+remains field-tested (Windows continuously; macOS and NixOS last
+field-tested with plugin v1.3 — later versions are covered there by
+the test suites only).
 
 ## Setup (one-time)
 
 The plugin is developed and tested on **Windows**; **macOS works**
-(field-tested on KiCad 10 after a round of mac-specific fixes), and
-**Linux works** (field-tested on NixOS — the hardest Linux to run pip
-wheels on; mainstream FHS distributions should be no harder, reports
-welcome). KiCad builds the plugin a private Python venv from
+(field-tested on KiCad 10 after a round of mac-specific fixes, last
+with plugin v1.3), and **Linux works** (field-tested on NixOS — the
+hardest Linux to run pip wheels on, last with plugin v1.3; mainstream
+FHS distributions should be no harder, reports welcome). KiCad builds the plugin a private Python venv from
 `requirements.txt` on every platform, from pre-built wheels only, no
 compiler needed. Steps 1–4 are the same everywhere; OS specifics are
 spelled out per step and in *Platform notes* below.
@@ -110,7 +111,8 @@ spelled out per step and in *Platform notes* below.
 - **Windows** is the development and test platform — everything in
   this README was exercised here. KiCad's bundled Python is 3.13, so
   the venv gets the current dependency stack.
-- **macOS** — **works** (field-tested on KiCad 10). Requires
+- **macOS** — **works** (field-tested on KiCad 10, last with plugin
+  v1.3). Requires
   macOS 12+ (KiCad's own minimum; Intel and Apple Silicon — the dmg
   is universal). KiCad's bundled Python is **3.9**, so pip resolves
   an older stack (numpy 2.0, scipy 1.13, matplotlib 3.9,
@@ -119,8 +121,9 @@ spelled out per step and in *Platform notes* below.
   Plot and dialog windows may open **behind** the KiCad window (they
   are raised best-effort) — check the Dock if nothing seems to appear
   after a solve.
-- **Linux** — **works** (field-tested on NixOS, KiCad 10; mainstream
-  distributions are audited but not yet field-tested). The venv uses
+- **Linux** — **works** (field-tested on NixOS, KiCad 10, last with
+  plugin v1.3; mainstream distributions are audited but not yet
+  field-tested). The venv uses
   the system Python (3.9+), so the stack matches your distribution.
   On **ARM64 (aarch64)** there are no pyamg wheels —
   `requirements.txt` skips pyamg there and the solver falls back to
@@ -236,7 +239,10 @@ the picked file. **Save config…** asks for the target file name each
 time (pre-filled with the loaded config), so writing back and saving
 a variant under a new `fill_res_config.<name>.json` are both one
 click — a name outside the auto-load set prints a reminder that it
-needs Load config….
+needs Load config…. The dialog opens even when nothing on the board
+yields a setup (nothing selected, no marker rectangles, no config):
+load-only, with both mode radios disabled and their reasons shown, so
+**Load config…** can bootstrap the run.
 
 **Precedence**: `config.py` constants < config file < dialog edits.
 The file pre-fills the dialog; what the dialog shows is what runs. A