docs: fix readme inconsistencies and expand DSL documentation

[Copilot]

The readme contained a typo, an outdated claim about JavaScript support, and a misleading "Generated artifacts" section that showed door-event/door-state output immediately after a my-type/another-class code example — with no indication they were unrelated.

Fixes

• Typo: "of if" → "or if"
• Stale info: "soon javascript" — JS is fully implemented and now listed as supported

Restructured & expanded content

• Separated examples: my-type/another-class usage example now shows its own generated Swift/Kotlin/JavaScript output; door-state-machine artifacts moved to a dedicated ## Example: Door State Machine section with a link to the example file
• Kotlin output: corrected class AnotherClass {} → class AnotherClass{} to match actual codegen
• Constructor argument options: documented :name and :array opts, and the :class vs :datatype kind distinction — previously only visible by reading source
• register-class: added usage example for registering a standalone class as a top-level artifact
• generate-artifact / compile-artifact API: added minimal usage snippet with supported targets listed
• Installation: Quicklisp setup instructions
• Running tests: make tests

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