.md skill added to get fsharp-diagnostics (like IDE does, via FsharpChecker)

[T-Gro]

The idea of this is skill is to provide much faster syntax and semantical errors, as opposed to agent always doing dotnet build or build script.
In sessions with multiple change-fix iterations, this pays off.
In the happy path, this does add overhead since separate compilation needs to happen afterwards anyway.

A working language-agnostic LLM2LSP solves this and is conceptually much better, so this is (hopefully) very ephemeral and tailored to this repo only, until a generic mechanism works everywhere.

(but do feel free to copy it, experiment and provide feedback even for your project - the number of hardcoded assumptions is low and easily re-vibe-code-able.)

Warmup (clean project)

┌────────┬───────────────────────────┐
│ Metric │ Value                     │
├────────┼───────────────────────────┤
│ Result │ OK (0 errors, 0 warnings) │
├────────┼───────────────────────────┤
│ Time   │ 73s                       │
├────────┼───────────────────────────┤
│ RAM    │ 2,058 MB                  │
└────────┴───────────────────────────┘

Parse-only (3 files, after warmup)

┌──────────────────┬──────┬───────────────────┐
│ File             │ Time │ Result            │
├──────────────────┼──────┼───────────────────┤
│ CheckBasics.fs   │ 70ms │ OK                │
├──────────────────┼──────┼───────────────────┤
│ CheckPatterns.fs │ 78ms │ OK                │
├──────────────────┼──────┼───────────────────┤
│ LowerCalls.fs    │ 72ms │ 2 syntax errors ✓ │
└──────────────────┴──────┴───────────────────┘

Full typecheck (change 3 files, but rest stays cached)

┌──────────────────┬───────┬──────────────────────────────┐
│ File             │ Time  │ Result                       │
├──────────────────┼───────┼──────────────────────────────┤
│ CheckBasics.fs   │ 395ms │ ERROR FS0001 type mismatch ✓ │
├──────────────────┼───────┼──────────────────────────────┤
│ CheckPatterns.fs │ 404ms │ ERROR FS0039 undefined ✓     │
├──────────────────┼───────┼──────────────────────────────┤
│ LowerCalls.fs    │ 425ms │ 2 parse errors ✓             │
└──────────────────┴───────┴──────────────────────────────┘

Full project (after individual checks)

┌──────────────┬─────────────────────────┐
│ Metric       │ Value                   │
├──────────────┼─────────────────────────┤
│ Time         │ 1.1s                    │
├──────────────┼─────────────────────────┤
│ Errors found │ 3 files, 5 errors total │
├──────────────┼─────────────────────────┤
│ RAM          │ 3,254 MB                │
└──────────────┴─────────────────────────┘

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