fix: report propertyNames errors on the offending key

[tarunagnihotri534]

Fixes #151

What this fixes

When a schema used propertyNames and a document had a key that failed it, the real validation error was never reported on that key. Instead, the server showed "Invalid JSON Pointer" on the document's $schema line.

Root cause

In SchemaValidationDiagnosticsProvider.ts:

• For propertyNames violations, @hyperjump/json-schema reports instanceLocation as #*<pointer> (for example #*/123 or #*/nested/123).
• Slicing off the # left */123, which was passed to jsonDocument.findNodeAtPointer. Since it doesn't start with /, @hyperjump/json-pointer threw Invalid JSON Pointer.
• The outer catch attached that message to /$schema, and the real diagnostic was never created.

Changes

• Use the existing toPointer helper instead of decodeURIComponent(error.instanceLocation.slice(1)). It already strips the leading *.
• Report on the key, not the value. When instanceLocation starts with #* and the resolved node belongs to a property, the diagnostic is attached to the property's key node (node.parent.children[0]).
• The generic catch fallback is unchanged.

Tests

Added to SchemaValidationDiagnosticsProvider.test.ts:

• a key failing propertyNames gets a diagnostic on that key, and none on $schema
• multiple failing keys each get their own diagnostic
• a failing key inside a nested object is placed correctly
• keys that need JSON Pointer escaping (/ and ~) are placed correctly
• a document whose keys all pass produces no diagnostics

I confirmed the first test failed before the fix, with "Invalid JSON Pointer" reported on $schema.

Testing

• vitest run: 20 files, 465 tests pass
• tsc --noEmit: no errors
• oxlint src: 0 warnings, 0 errors

Notes

• This is independent of fix: clear diagnostics when a document is closed #152 and branches from main, so the two shouldn't conflict.
• I used an AI coding agent (Antigravity with Gemini) to help find this issue and draft the change. I reviewed the diff and ran the tests myself.

[jdesrosiers]

This is the wrong approach. Update JsonDocument.findNodeAtPointer to understand the * syntax. Then it will work everywhere, not just for schema validation diagnostics.