fix(eve): protect nitro-referenced dev snapshots

[iroiro147]

Summary

• protect stale dev-runtime snapshots that are still referenced by generated .eve/nitro artifacts
• keep existing pointer and active workflow-data protections intact while allowing unrelated stale snapshots to prune
• add regression coverage for an aggressive prune that preserves a Nitro-referenced snapshot

Refs #534.

Tests

• pnpm install (completed; hook installer printed an ENOTDIR warning because this checkout is a Git worktree)
• pnpm --filter eve run test:integration -- src/internal/nitro/dev-runtime-artifacts.integration.test.ts -t 'generated Nitro files' (50 files passed, 386 tests passed)
• pnpm --filter eve run typecheck
• pnpm guard:invariants
• pnpm exec oxfmt --check packages/eve/src/internal/nitro/dev-runtime-artifacts.ts packages/eve/src/internal/nitro/dev-runtime-artifacts.integration.test.ts .changeset/dev-runtime-nitro-prune-protection.md
• pnpm exec oxlint packages/eve/src/internal/nitro/dev-runtime-artifacts.ts packages/eve/src/internal/nitro/dev-runtime-artifacts.integration.test.ts
• git diff --check
• pnpm changeset status --since origin/main

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