Add v0.1 scaffold: tree-sitter-p8-cart grammar and Zed extension

The grammar parses the .p8 cartridge container ( header, version, and
the named __lua__/__gfx__/__gff__/__label__/__map__/__sfx__/__music__
sections, plus a fallback unknown_section ). The Zed language definition
hands the __lua__ body to Zed's built-in Lua via injections.scm, so
non-dialect Lua code highlights correctly today; PICO-8-specific syntax
(?, +=, !=, single-line if, etc.) will fall back to error highlighting
in those regions only — see README roadmap for the dialect grammar fork.

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

extension.toml

@@ -0,0 +1,15 @@
+id = "pico-8"
+name = "Pico-8"
+version = "0.0.1"
+schema_version = 1
+authors = ["Kistaro Windrider <kistaro@gmail.com>"]
+description = "Pico-8 cartridge (.p8) and Lua dialect support for Zed"
+repository = "https://github.com/kistaro/zed-p8"
+
+# The .p8 cart container grammar lives at the root of this repo.
+# During local development, set `repository` to `file://` + the absolute
+# path of your clone and pin `rev` to a committed SHA. When publishing,
+# this should point at a public Git URL.
+[grammars.p8_cart]
+repository = "file:///Users/norberg/gitea-repos/zed-p8"
+rev = "HEAD"