Fix lint baseline where possible

[powerje]

Summary

• Migrate 7 dialog editors (Toast, Ack, Script, Gag, Replace, Notification, NewConnection) from Java/XML to Kotlin/Compose with shared EditorDialogScaffold
• Delete 15 dead layout XML files and 31 duplicate drawable assets across density buckets
• Fix ~500 mechanical lint issues: ContentDescription, Autofill, LabelFor, TextFields, ObsoleteLayoutParam, ButtonStyle, HardcodedText, UselessParent, Overdraw, RtlHardcoded, Deprecated, SpUsage, CutPasteId, MissingPrefix, SuspiciousIndentation, PluralsCandidate, MissingClass
• Fix manifest class reference (com.happygoatstudios.bt → com.offsetnull.bt for MainWindow)

Remaining 9 baseline issues

• AndroidGradlePluginVersion (3) — AGP/Gradle upgrades tracked in issue #78
• OldTargetApi (1) — targetSdk 35 is current; lint wants 36 which isn't stable
• IconDensities (2) + IconMissingDensityFolder (1) — need xhdpi/xxhdpi drawable assets
• SuspiciousIndentation (1) — persistent in MainWindow.java, may be false positive

Test plan

• ./gradlew :BT_Free:assembleDebug builds successfully
• App installs and launches on Pixel 10
• Manual smoke test: launcher screen loads, connections list renders