solid-v2: make Oxlint configs editor-discoverable

[brenelz]

Summary

• rename Solid 2 Oxlint configs to the auto-discovered oxlint.config.ts filename
• remove explicit -c flags from template lint scripts
• allow Oxlint editor integrations to load the Solid rules without workspace-specific settings

Verification

• pnpm exec prettier --check "solid-v2/*/oxlint.config.ts" "solid-v2/*/package.json"
• pnpm exec tsc --noEmit in a generated fullstack project
• confirmed pnpm exec oxlint src/server/test.ts reports the expected Solid diagnostic without an explicit config flag