fix(web): unreadable synced rows drop instead of crashing; stale tabs reload onto a new build - #2340

🟢 Confidence 10/10 · safe to merge. No defect in the non-throwing row decode or the reload guard; the riskiest part, the once-per-commit reload, is pinned by the new shell tests.
_{no findings · tests covered · risk medium · 2/2 new units observable}

Synced rows this build cannot decode now drop and are reported instead of throwing out of live-query callbacks, and a stale tab probes /version.json on a chunk-load failure or dropped row, reloading a hidden tab with no unsaved work at most once per deployed commit. Safe to merge.

• liveRowDecoder decodes a whole row to Option, dropping and reporting unreadable rows
• rowsTo* helpers filter dropped rules, incidents and API keys at every call site
• Chunk-load and undecodable-row signals probe /version.json in a StaleBuildProbe span
• A hidden tab with no unsaved work reloads once per deployed commit; blocked storage falls back to the banner

Production impact

_{d78026a · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}