Use idiomatic Effect decoding for VCS config

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What Changed

• Decode .t3code/vcs.json with Schema.fromJsonString / Schema.decodeUnknownOption instead of manual JSON.parse plus a schema guard.
• Use Option internally for missing VCS config paths and unreadable config contents.
• Represent the workspace entries cache TTL as Duration.seconds(15) instead of a millisecond constant.
• Added regression coverage for malformed VCS config JSON.

Why

These are small Effect idiom improvements that keep config parsing schema-driven, make absent values explicit, and avoid raw duration numbers in cache policy code.

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 Option decoding for VCS project config

• Replaces manual JSON.parse + try/catch in VcsProjectConfig.ts with Effect's Schema.fromJsonString and Schema.decodeUnknownOption, returning Option types throughout.
• findConfigPath and readConfiguredKind now return Option<string> and log a warning on read failure instead of returning null.
• Adds a test case for malformed JSON in .t3code/vcs.json, asserting resolveKind falls back to 'auto'.
• Replaces WORKSPACE_CACHE_TTL_MS number constant with Duration.seconds(15) in WorkspaceEntries.ts.

^{Macroscope summarized 0593260.}