Refactor server diagnostics with Effect-native APIs

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What Changed

• Replaced Node fs/promises and Effect.tryPromise in workspace file reads with the injected Effect FileSystem, scoped handles, FileSystem.Size, and Option.
• Replaced unchecked Windows process JSON.parse/record traversal with Schema.fromJsonString, per-record Schema decoding, and Option normalization.
• Added focused coverage for bounded file previews, normalized platform errors, Windows arrays/singletons, invalid records, and malformed JSON.

Why

These paths now stay inside Effect APIs end-to-end, making filesystem behavior layer-testable and process payload parsing typed and explicit while preserving existing behavior.

Checklist

• This PR is small and focused
• I explained what changed and why
• UI changes are not applicable

  

Note

Refactor server diagnostics and workspace file reading to use Effect-native APIs

• Rewrites parseWindowsProcessRows in ProcessDiagnostics.ts to use Schema-based decoding, skipping invalid records and returning [] for malformed JSON. The function is now exported.
• Rewrites readFile in WorkspaceFileSystem.ts to use the Effect FileSystem service for realPath, open, stat, and readAlloc, replacing direct node:fs/promises calls.
• Behavioral Change: readFile error causes are now PlatformError values instead of NodeJS.ErrnoException; resource management is scoped rather than manual close.

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