Improve error messages and defensive runtime checks across component factories

[blackopsrepl]

Summary

Strengthen runtime error handling and consumer-facing diagnostics across the library.

Problem

Several APIs assume happy-path configuration and fall back to generic browser errors when something is missing or invalid. Production libraries should fail clearly and point consumers to the real integration mistake.

Scope

• Audit component factories and adapter entry points for unclear failures
• Replace generic throws and null-reference crashes with targeted error messages
• Add validation for required inputs, mount roots, and backend configuration
• Document the expected failure modes where useful

Acceptance Criteria

• Misconfigured mounts fail with clear actionable errors
• Invalid or incomplete configuration is detected before deeper runtime failure
• Error text identifies the affected API surface and the missing or invalid input
• Tests cover representative misconfiguration scenarios

Notes

This issue pairs well with the backend-contract and test-coverage work.

[blackopsrepl]

Resolved by merged PR #23: #23

What shipped:

• SF.assert was added for consistent runtime errors
• component/backend/solver factories now validate required config and callbacks more clearly
• Gantt mount/root checks and related defensive guards were added
• compatibility regressions were fixed before merge so existing non-Tauri backend labels and default SF.gantt.create() construction still work

Closing this issue because the runtime diagnostics and validation work is merged on main.