Add readline, color, http_post_auth builtins; fix import resolution in build

Engram can now power the Neuron CLI:

- readline(prompt) -> String: interactive terminal input via stdin
- http_post_auth(url, token, body) -> String: authenticated POST for daemon API
- color_cyan/green/red/yellow/bold/dim(s) -> String: ANSI color output
  All registered in el-types type checker

- el build now resolves import "file.el" directives recursively (was only
  done for el run-file and el check; project builds failed silently)

- Add .gitignore (target/, *.elc, *.sealed, *.map.json)

.gitignore

@@ -0,0 +1,6 @@
+target/
+*.elc
+*.sealed
+*.map.json
+.el/
+.claude/