fix(dashboard): prevent mobile experiment table clipping

[christso]

Summary

• Wrap the Experiments tab table in a mobile-safe horizontal overflow container.
• Give the table a fixed minimum width and nowrap behavior, matching the recent Targets tab pattern.
• Keep the existing desktop table layout and column order unchanged.

Fixes #1351

Verification

• cd apps/dashboard && bun run build
• bun --filter @agentv/dashboard test
• bun run lint
• bun run build && bun run test

Manual red/green UAT

Tested with a local fixture served via bun apps/cli/src/cli.ts dashboard --single --dir /tmp/agentv-1351-uat --port 4117 after rebuilding Dashboard static assets.

• Red before fix: /tmp/agentv-1351-evidence/red-experiments-mobile.png — wrapper was overflow-hidden; viewport wrapper width was 340px while table content was 609px, so right-side columns were clipped.
• Green after fix: /tmp/agentv-1351-evidence/green-experiments-mobile.png — wrapper is overflow-x-auto; horizontal scroll is available.
• Green scrolled right: /tmp/agentv-1351-evidence/green-experiments-mobile-scrolled-right.png — verified the table scrolls to the right-side metrics on a 390px mobile viewport.

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