Make diagnostics parsing more idiomatic Effect

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What Changed

• Updated trace diagnostics NDJSON line parsing to use the shared decodeJsonResult(Schema.Record(...)) helper instead of JSON.parse.
• Kept trace timestamp parsing and aggregate span bounds as Option values internally until returning the diagnostics result.
• Updated process diagnostics so ProcessRow.pgid is represented as an Option and Windows PowerShell JSON parsing goes through Effect Schema decoding.
• Added Windows process parsing coverage and updated process diagnostics tests to use assert from @effect/vitest.

Why

These changes address focused places where diagnostics code was already Effect-based but still used ad-hoc JSON parsing and nullable internal fields. Using Schema-backed JSON decoding and Option makes the parsing boundaries more testable and consistent with the rest of the Effect codebase while preserving the existing soft-fail diagnostics behavior.

UI Changes

Not applicable; this is a server diagnostics refactor with no UI changes.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Validation:

• pnpm exec vp test run src/diagnostics/TraceDiagnostics.test.ts src/diagnostics/ProcessDiagnostics.test.ts src/diagnostics/ProcessResourceMonitor.test.ts (from apps/server) — 17 tests passed
• pnpm exec vp check --fix — passed with existing warnings
• pnpm exec vp run typecheck — passed

  

Note

Refactor diagnostics parsing to use Effect Option types instead of nullables

• Changes the pgid field on ProcessRow from number | null to Option.Option<number> across ProcessDiagnostics.ts, ProcessResourceMonitor.test.ts, and related tests.
• Replaces JSON.parse with schema-based decoding (Schema, decodeJsonResult) in both parseWindowsProcessRows and aggregateTraceDiagnostics, so invalid JSON or malformed records now return empty results or are skipped rather than throwing.
• Introduces typed WindowsProcessRecord schema with stricter validation: ProcessId must be a positive integer, ParentProcessId must be non-negative, and status defaults to 'Live' when absent.
• Replaces nullable helper functions in TraceDiagnostics.ts with Option-returning variants throughout span aggregation logic.
• Behavioral Change: Windows process rows with non-integer or out-of-range IDs are now silently dropped; non-JSON input to parseWindowsProcessRows now yields [] instead of throwing.

^{Macroscope summarized b5d4e92.}