Doctor: Port layout-neutral check to TypeScript

[normenmueller]

Context

Migrate the scaffold check cli/src/lib/doctor/_scaffold/checks/layout-neutral.sh to a native TypeScript module at cli/src/lib/doctor/checks/layout-neutral.ts.

Acceptance Criteria

• cli/src/lib/doctor/checks/layout-neutral.ts exports validate(corpusRoot: string): DiagnosticResult[]
• Check verifies that capability directory layout follows the prescribed structure (no unexpected files or directories)
• Check verifies naming conventions (kebab-case, no uppercase, no spaces)
• ai4x doctor invokes the new check (replaces scaffold invocation)
• Scaffold counterpart (layout-neutral.sh) deleted after port
• Tests cover: valid layout (pass), unexpected file in domain dir (fail), invalid naming (fail)

Technical Notes

• Pure function: corpus path in, diagnostics out
• DiagnosticResult schema as defined in the doctor module
• The shell script uses find/grep; TypeScript port must replicate the same traversal and pattern logic
• Reference implementation: cli/src/lib/doctor/_scaffold/checks/layout-neutral.sh