Feature/cross file validation

[jtgreen86]

What this adds

Cross-file validation for Splunk .conf files: catches broken references between related configuration files before deployment. These issues are syntactically valid but cause silent runtime failures or unexpected behavior in production.

Problems it catches

• Broken transform references (e.g. REPORT-foo = my_transform in props.conf but [my_transform] doesn't exist in transforms.conf)
• Missing lookup files (e.g. filename = users.csv in transforms.conf but the file doesn't exist in lookups/)
• Invalid index references (e.g. index = custom_index but the index isn't defined in indexes.conf)
• Undefined sourcetypes (data inputs with sourcetypes that have no parsing rules defined)
• Orphaned configurations (transform stanzas that are defined but never referenced)

Files added

File	Purpose
out/crossFileValidator.js	All cross-file validation logic
out/workspaceScanner.js	Utilities for navigating Splunk app directory structures
test/crossFileValidator.test.js	Unit tests for all validators (70 total)
test/workspaceScanner.test.js	Unit tests for workspace scanner
test/setup.js	Global test setup with VS Code mocks
test/mocks/vscode.js	Mock VS Code API for testing

Files modified

File	What changed
out/extension.js	Added crossFileValidator import, integrated all validators into getDiagnostics()
out/codeActionProvider.js	Added createCrossFileActions() method with quick fixes for each diagnostic type
package.json	Added 7 cross-file validation configuration settings
README.md	Added cross-file validation to feature list with configuration docs
CHANGELOG.md	Added cross-file validation features to 0.4.0 entry

Notes

• Respects Splunk's default/ and local/ configuration layering to prevent false positives
• Master toggle plus individual toggles for each validator via splunk.crossFileValidation.* settings
• splunkHome setting enables validation against system-level configurations
• Orphaned stanzas use VS Code's DiagnosticTag.Unnecessary for subtle faded styling
• All 70 tests passing
• No existing functionality was modified (syntax validation, semantic linting, etc. unchanged)