Fix V2 memory deletion, Workflow import, and test scope

[zszz3]

What changed

• prevent workspace deletion from interrupting an in-flight OpenViking read and surfacing a misleading failure
• serialize OpenViking runtime-state cleanup so an immediate child-process exit preserves the real startup error
• accept the intentionally empty legacy Workflow execution route when importing a Workflow exported by the current version
• prune redundant V2 test suites while preserving the Runtime Agent integrity regressions added on the latest main

Why

Workspace cleanup could complete successfully while a concurrent search failed with fetch failed. OpenViking's startup-state file could also be deleted between writing and securing it when the child process exited immediately, masking the underlying startup error. Separately, the Runtime Agent integrity change intentionally leaves the deprecated top-level Workflow route empty, but the portable-file parser still rejected that current-format export. The V2 suite had also grown well beyond the desired CI signal-to-noise ratio.

Impact

• Memory workspace deletion no longer looks failed because a background read was quiesced.
• OpenViking startup failures report their actual cause instead of an intermittent missing-state-file error.
• A Workflow exported by the current version can be imported again.
• V2 now runs 1,079 Vitest checks plus 118 script checks, 1,197 total.

Validation

• npm test in apps/main-2.0: 1,197 passed
• npm run build in apps/main-2.0
• npm run release-note:check