Improve error details with richer diagnostic information

[kmcginnes]

Description

The Error Details dialog previously showed only the error name and message, which often duplicated the user-friendly display error without adding diagnostic value. This change makes the details dialog genuinely useful for troubleshooting by surfacing status codes, response data, cause chains, and structured validation errors.

• Extract createErrorDetails from ErrorDetailsButton into a standalone tested function
• Show HTTP status code and standard status text for NetworkError (e.g., "500 Internal Server Error")
• Add statusText property to NetworkError backed by an HTTP_STATUS_TEXT lookup
• Display response body data as formatted JSON in a code editor when available
• Surface error.cause chains with all own properties (excluding stack traces)
• Show ZodError issues as structured JSON in the data field
• Extract extractErrorMessage to generically pull messages from error response bodies using detailedMessage, message, description, or error fields
• Remove Neptune-specific NeptuneErrorSchema in favor of the generic extractErrorMessage approach
• Add text-muted-foreground to Label for better visual distinction in the dialog

Validation

• pnpm run checks passes (lint, format, types)
• pnpm test passes (1483/1483 tests across 141 files)
• 35 tests for createErrorDetails covering NetworkError, ZodError, DOMException, Error with cause chains, and non-Error values
• 11 tests for extractErrorMessage covering all key priorities and edge cases

Related Issues

• Fixes Improve error details to show more useful diagnostic information #1643

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have verified pnpm checks passes with no errors.
• I have verified pnpm test passes with no failures.
• I have covered new added functionality with unit tests if necessary.
• I have updated documentation if necessary.

[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.04%. Comparing base (c5affc5) to head (3820449).
⚠️ Report is 119 commits behind head on main.

Files with missing lines	Patch %	Lines
...aph-explorer/src/connector/fetchDatabaseRequest.ts	0.00%	1 Missing and 1 partial ⚠️
...kages/graph-explorer/src/components/PanelError.tsx	80.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1644       +/-   ##
===========================================
+ Coverage   47.81%   63.04%   +15.23%     
===========================================
  Files         382      396       +14     
  Lines        8525     9235      +710     
  Branches     3159     3514      +355     
===========================================
+ Hits         4076     5822     +1746     
+ Misses       3070     2368      -702     
+ Partials     1379     1045      -334     

Flag	Coverage Δ
unittests	63.04% <93.75%> (+15.23%)	⬆️

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