Use more idiomatic Effect APIs in VCS config and diagnostics

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What Changed

• Decode .t3code/vcs.json through Schema.fromJsonString instead of JSON.parse plus manual schema checks.
• Return Option from VCS config discovery/read failure paths instead of null sentinels.
• Run the process resource sampler with Duration/Schedule primitives instead of a manual millisecond sleep loop.
• Added a regression test for invalid VCS config fallback behavior.

Why

These are small, production-path improvements that align the codebase with idiomatic Effect patterns while preserving existing fallback behavior.

UI Changes

None.

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

  

Note

Use idiomatic Effect APIs in VCS config and diagnostics

• Replaces the manual JSON.parse + Schema.is guard in VcsProjectConfig.ts with Schema.decodeUnknownEffect and Effect.option for cleaner decode-or-fallback logic
• Refactors findConfigPath to return Option<string> and readConfiguredKind to return Option values, eliminating nullable returns
• Replaces the manual forever + sleep loop in ProcessResourceMonitor.ts with Effect.repeat(Schedule.spaced(SAMPLE_INTERVAL))
• Adds a test case for invalid VCS config JSON, asserting resolveKind falls back to 'auto'

^{Macroscope summarized 4419ba0.}