[pitill0]

Summary

• Defer loading administration, station import, remote subscription, and custom station controllers until their first use.
• Preserve session safety, dialog navigation, and controller lifecycle behavior during asynchronous loading.
• Improve recovery feedback when track metadata requests fail, while retaining existing metadata and bounded polling.
• Add regression coverage for deferred controllers, session changes, concurrent interactions, and metadata retry behavior.

Validation

• 1,907 tests passed; 8 skipped.
• Ruff, Mypy, Bandit, JavaScript syntax checks, and Git diff validation passed.
• Browser validation completed for all four deferred controllers.
• Initial JavaScript gzip size reduced by 9.41% (approximately 5.5 KB).
• Under simulated mobile network conditions, median page-load time improved by approximately 54 ms across six cold-load runs per version.
• No measurable improvement demonstrated on localhost; network benchmark results are indicative rather than universal.

Closes #314