docs: fix Vale contraction lint + reflect hard-failure behavior

Use contractions (doesn't / that's) to satisfy the Microsoft.Contractions
rule in the developer-guide quality gate, and update the wording from
"logs a warning" to "fails the build" to match the new behavior.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: shai-almog

docs/developer-guide/Miscellaneous-Features.asciidoc

@@ -458,9 +458,9 @@ cn1_icon_<lang>[_<country>].png
 * `cn1_icon_en_GB.png`: British English
 * `cn1_icon_es_MX.png`: Mexican Spanish
 
-Supply a square source image at least 432×432 pixels (the largest size emitted for Android adaptive icons; 1024×1024 is recommended, matching the main app icon); the build resizes it to every target density. A smaller source is upscaled and will look blurry — the build now logs a warning when it detects an undersized localized icon. The default app icon continues to be controlled by your `codenameone_settings.properties` file and is used whenever the device locale doesn't match any of the localized variants.
+Supply a square source image at least 432×432 pixels (the largest size emitted for Android adaptive icons; 1024×1024 is recommended, matching the main app icon); the build resizes it to every target density. A smaller source would be upscaled and look blurry, so the build now fails with a clear error when it detects an undersized localized icon rather than shipping a soft one. The default app icon continues to be controlled by your `codenameone_settings.properties` file and is used whenever the device locale doesn't match any of the localized variants.
 
-NOTE: These icons live under `src/main/resources` and Maven copies them into `target/classes` incrementally — it does *not* delete the copy when you remove or rename the source file. If you replace a localized icon and still see the old (often blurry) one, run `mvn clean` to clear the stale resource from `target/classes` before rebuilding. The build also warns when it finds an undersized `cn1_icon_*.png` in the compiled output that is about to be bundled and sent to the build server.
+NOTE: These icons live under `src/main/resources` and Maven copies them into `target/classes` incrementally — it *doesn't* delete the copy when you remove or rename the source file. If you replace a localized icon and still see the old (often blurry) one, run `mvn clean` to clear the stale resource from `target/classes` before rebuilding. The build also fails when it finds an undersized `cn1_icon_*.png` in the compiled output that's about to be bundled and sent to the build server.
 
 At runtime the builders look for a `<lang>_<COUNTRY>` match first, then fall back to a bare `<lang>` match. Providing both (for example `cn1_icon_en.png` plus `cn1_icon_en_GB.png`) lets you give British users a country-specific icon while every other English locale still receives the generic English icon.