feat: support negative qualifiers in queries

[Djain912]

Summary

Implements issue #24 by adding support for negative qualifiers in matching queries.

What changed

• Added shared negative-query parsing for not, excluding, and except.
• Added exclusion-context matching against element metadata (section, parent, name, role, value, labelled_by).
• Wired exclusion filtering into lexical and embedding matchers (combined inherits this behavior automatically).
• Added focused and edge-case tests, including duplicate-label disambiguation scenarios.
• Added docs/examples in README and CLI reference.

Example queries now supported

• submit button not in header
• login link, not the footer one
• search box excluding sidebar

Validation

• go test ./internal/engine -run "TestParseNegativeConstraints_BasicPatterns|TestShouldExcludeElement_ContextSignals|TestLexicalMatcher_NegativeQualifierFiltersExcludedSection|TestEmbeddingMatcher_NegativeQualifierFiltersSidebarVariant|TestCombinedMatcher_NegativeQualifier_RealWorldDuplicateLinks" -count=1
• go test ./internal/engine -run "TestComprehensiveEvaluation|TestMultiSiteEvaluation" -count=1 -v
• go test -count=1 ./...
• go vet ./...
• go build ./...
• go build -o semantic.exe ./cmd/semantic
• go run github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.9.0 run
• Manual CLI checks with duplicate section variants (header/footer/sidebar)

Environment note

• Local Windows race run (go test -race ./...) is blocked by local 64-bit cgo toolchain availability (cc1.exe ... 64-bit mode not compiled in).
• CI runs on Ubuntu and will execute race tests there.

Closes #24

[luigi-agosti]

this pr was partially already implemented I extracted and added to a separated pr the context/region exclusion support only