fix: add actionable config and state errors

[flexdinesh]

• Behavior owner and change: config errors include nested JSON, exact key moves and accepted values; reviewstore errors identify database/backup paths, compatible schemas and --state recovery.
• Contracts: rejected config/state stays unchanged; examples never echo credentials. Tests cover recovery in local and remote modes.
• Validation: mise run check and pre-push mise run check:push passed, including Go race tests and 75 browser tests. Generated assets unchanged.
• Architecture: document actionable diagnostics; persistence and mode policies unchanged.
• UI evidence: not applicable.