[rokath]

Headings such as Xxxx_Yyyy and inline-code identifiers such as __COUNTER__ now retain their authored text and formatting in the generated ToC. Link labels use the original title markup with safe bracket escaping, while slug generation independently preserves literal/escaped identifier characters and decodes entities outside code.

Adds regression coverage for all three slug profiles, anchor and numbering options, regeneration, and file-based generate/strip/check workflows. Updates the specification and prepares v1.0.3 with matching CLI/extension release notes and extension version files.

Validation:

• go test ./... -coverprofile=coverage.out (280 passing tests/subtests)
• go vet ./...
• go build -o dist/mdtoc.exe ./cmd/mdtoc
• Extension: npm ci, npm run check, npm run build
• Compared 13 generated link labels with their original headings using the extension toolchain's Markdown renderer; rendered contents match.

Closes #123.