v0.2: Pico-8 Lua dialect grammar and language

Reorganize into grammars/<name>/ subdirs ( Zed's [grammars.*] supports
a `path` field, so both grammars ship from this repo without a sibling-
repo split ). Vendor tree-sitter-lua as the fork base for tree-sitter-
pico8-lua; upstream MIT license preserved at grammars/pico-8-lua/
UPSTREAM-LICENSE.md.

Dialect features added: != as ~= alias, \ integer divide, ^^ binary xor,
>>> / <<> / >>< shifts and rotates, compound-assignment statements,
memory peek prefixes @ % $ (% coexists with binary modulo), single-line
`if (cond) stmt [else stmt]` and `while (cond) stmt`, statement-level
print shorthand ?, and `#include path` directives. Identifier rule no
longer accepts ! ? @ $ ( upstream did ).

Pico-8 Lua language ( languages/pico-8-lua/, suffix .p8lua ) ships
highlights with the full ~110 PICO-8 builtins as @function.builtin.
The cart injection now hands __lua__ bodies to pico-8-lua, so .p8 carts
and bare .p8lua files share the dialect-aware grammar. Examples updated
to exercise the dialect end-to-end.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

languages/pico-8-cart/injections.scm

@@ -1,11 +1,5 @@
-; Inject Lua syntax highlighting into the __lua__ section.
-;
-; NOTE: This injects Zed's built-in Lua grammar, which does not
-; understand Pico-8 dialect extensions ( ?, +=, !=, single-line
-; `if (cond) stmt`, binary literals, memory peek prefix operators,
-; etc. ). Code that uses those forms will produce parse errors
-; locally, with degraded highlighting in those regions only — the
-; rest of the file will still render correctly. A future Pico-8
-; Lua grammar fork will replace this; see README for status.
+; Hand the body of the __lua__ section to the Pico-8 Lua grammar so the
+; dialect-aware parser parses it (compound-assignment statements, the `?`
+; print shorthand, single-line `if (cond) stmt`, peek prefixes, etc.).
 ((lua_content) @injection.content
- (#set! injection.language "lua"))
+ (#set! injection.language "pico-8-lua"))