feat: add devtools (tree-sitter, neovim, formatter, CLI commands)

- Add tree-sitter grammar for syntax highlighting
- Add Neovim plugin with syntax, LSP integration, and commands
- Add code formatter (lux fmt) with check mode
- Add CLI commands: fmt, check, test, watch, init
- Add project initialization with lux.toml template

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

editors/nvim/syntax/lux.vim

@@ -0,0 +1,89 @@
+" Vim syntax file for Lux
+" Language: Lux
+" Maintainer: Lux Team
+
+if exists("b:current_syntax")
+  finish
+endif
+
+" Keywords
+syn keyword luxKeyword fn let type effect handler trait impl for import export
+syn keyword luxKeyword match if then else with run resume is
+syn keyword luxKeyword nextgroup=luxFunction skipwhite
+
+" Boolean literals
+syn keyword luxBoolean true false
+
+" Built-in types
+syn keyword luxType Int Float Bool String Char Unit Option Result List
+syn keyword luxType Some None Ok Err
+
+" Operators
+syn match luxOperator /[+\-*/%=<>!&|]/
+syn match luxOperator /==/
+syn match luxOperator /!=/
+syn match luxOperator /<=/
+syn match luxOperator />=/
+syn match luxOperator /&&/
+syn match luxOperator /||/
+syn match luxOperator /|>/
+syn match luxOperator /=>/
+
+" Delimiters
+syn match luxDelimiter /[(){}\[\],;:]/
+syn match luxDelimiter /|/ contained
+
+" Numbers
+syn match luxNumber /\<\d\+\>/
+syn match luxFloat /\<\d\+\.\d\+\>/
+
+" Strings
+syn region luxString start=/"/ skip=/\\./ end=/"/ contains=luxEscape,luxInterpolation
+syn match luxEscape /\\[nrt\\'"0{}]/ contained
+syn region luxInterpolation start=/{/ end=/}/ contained contains=TOP
+
+" Characters
+syn region luxChar start=/'/ skip=/\\./ end=/'/
+
+" Comments
+syn match luxComment /\/\/.*$/
+syn match luxDocComment /\/\/\/.*$/
+
+" Function definitions
+syn match luxFunction /\<[a-z_][a-zA-Z0-9_]*\>/ contained
+syn match luxFunctionCall /\<[a-z_][a-zA-Z0-9_]*\>\s*(/me=e-1
+
+" Type definitions and constructors
+syn match luxTypedef /\<[A-Z][a-zA-Z0-9_]*\>/
+
+" Module access
+syn match luxModule /\<[A-Z][a-zA-Z0-9_]*\>\./me=e-1
+
+" Effect signatures
+syn region luxEffectSig start=/with\s*{/ end=/}/ contains=luxType,luxDelimiter
+
+" Properties
+syn match luxProperty /\<is\s\+\(pure\|total\|idempotent\|commutative\|associative\)\>/
+
+" Highlight groups
+hi def link luxKeyword Keyword
+hi def link luxBoolean Boolean
+hi def link luxType Type
+hi def link luxOperator Operator
+hi def link luxDelimiter Delimiter
+hi def link luxNumber Number
+hi def link luxFloat Float
+hi def link luxString String
+hi def link luxEscape SpecialChar
+hi def link luxInterpolation Special
+hi def link luxChar Character
+hi def link luxComment Comment
+hi def link luxDocComment SpecialComment
+hi def link luxFunction Function
+hi def link luxFunctionCall Function
+hi def link luxTypedef Type
+hi def link luxModule Include
+hi def link luxEffectSig Special
+hi def link luxProperty PreProc
+
+let b:current_syntax = "lux"