Bump version to 1.4.0

[rovkinmax]

Summary

• Prepare the next minor Puber release: 1.4.0.
• Bump currentVersion in app/build.gradle.kts from 1.3.4 to 1.4.0.
• Release branch: release/1.4.0; intended post-merge tag: v1.4.0.

Compliance Review

• Compliance Review passed for release 1.4.0 on commit f618c0b11b7d7bc5262ca3e67e0a1657a42896b8.
• Reviewed diff contains only the version bump in app/build.gradle.kts.
• No compliance violations were found.

Verification

• ./tools/agentw :app:compileDevDebugKotlin :app:compileProdReleaseKotlin completed successfully during release preparation.
• PR creation node re-checked repository state before pushing: clean release/1.4.0 branch at f618c0b11b7d7bc5262ca3e67e0a1657a42896b8.

Skipped Checks / Notes

• Production signing artifacts and environment variables are not present locally, so production packaging with signing secrets was not locally proven.
• Per the Puber release guidance, missing local signing secrets should be reported but do not block this version-bump PR.
• Do not merge this PR or create v1.4.0 until the release workflow reaches the publication gate.