feat(ax): pass 1 — remove banned imports, AX naming, test coverage

Replace fmt/strings/encoding/json/path/filepath/os with dappco.re/go/core
primitives across all non-test source files. Add core as direct dep.
Rename cfg→configuration, ctxLen→contextLen, met→result. Add usage
example comments on all exported functions. Ensure all three test
categories (Good/Bad/Ugly) exist for every tested function.

Residuals for pass 2:
- server.go: os/exec (no c.Process() available) + os.Environ() (no core wrapper)
- internal/gguf: os retained for *os.File.Stat() via core.Fs.Open result

Co-Authored-By: Virgil <virgil@lethean.io>

discover.go

@@ -10,7 +10,7 @@ import (
 // structured information about each. Files that cannot be parsed are skipped.
 //
 //	models, err := rocm.DiscoverModels("/data/lem/gguf")
-//	for _, m := range models { core.Print(c, "%s %s ctx=%d", m.Name, m.Quantisation, m.ContextLen) }
+//	for _, model := range models { core.Print(c, "%s %s ctx=%d", model.Name, model.Quantisation, model.ContextLen) }
 func DiscoverModels(dir string) ([]ModelInfo, error) {
 	matches := core.PathGlob(core.Path(dir, "*.gguf"))