Allow an explicit no-accent value and stop OK from stepping settings

[zorenkonte]

Summary

Fixes the accent stripe appearing when the client had it switched off. The API had no way to say "no stripe" once the TV's default accent was set, and pressing OK on a settings row silently stepped its value, which is how the TV default got set in the first place.

Changes

• Treat an explicit empty accent as no stripe: accent sent as "none", "" or null now forces no stripe even when the TV has a default accent; omitting the field still means "use the TV default". Wrong types name the field in the 400 response. Two new parser tests; README field table updated.
• Send an explicit no-accent value from the client: the compose form sends "accent": "none" when the switch is off, so the preview matches the TV regardless of TV defaults. The blocked-send and unreachable messages now mention checking that the port is 8090, since a wrong port produced the same browser error as a mixed-content block.
• Stop OK from stepping settings values: settings rows only change on left and right; OK does nothing, matching the ◀ value ▶ hint.

Testing

• ./gradlew testDebugUnitTest assembleDebug: 59 tests pass, APK builds.
• npm run build && npm run lint clean.
• Verified on the code path that a payload with "accent": "none" reaches NotificationCardView.bind with accent == null, which hides the stripe.

Checklist

• cd tv && ./gradlew testDebugUnitTest assembleDebug passes
• cd client && npm run lint && npm run build passes
• No comments added to source files
• README updated when behavior, the API or setup changed
• Each commit is one logical change and builds on its own