Feat: documentation, UI/UX

crates/forth/README.md

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+# cagire-forth
+
+Stack-based Forth VM for the Cagire sequencer. Tokenizes, compiles, and executes step scripts to produce audio and MIDI commands.
+
+## Modules
+
+| Module | Description |
+|--------|-------------|
+| `vm` | Interpreter loop, `Forth::evaluate()` entry point |
+| `compiler` | Tokenization (with source spans) and single-pass compilation to ops |
+| `ops` | `Op` enum (~90 variants) |
+| `types` | `Value`, `StepContext`, shared state types |
+| `words/` | Built-in word definitions: `core`, `sound`, `music`, `midi`, `effects`, `sequencing`, `compile` |
+| `theory/` | Music theory lookups: `scales` (~200 patterns), `chords` (interval arrays) |
+
+## Key Types
+
+- **`Forth`** — VM instance, holds stacks and compilation state
+- **`Value`** — Stack value (int, float, string, list, quotation, ...)
+- **`StepContext`** — Per-step evaluation context (step index, tempo, variables, ...)
+- **`Op`** — Compiled operation; nondeterministic variants carry `Option<SourceSpan>` for tracing
+- **`ExecutionTrace`** — Records executed/selected spans and resolved values during evaluation