feat: unified testing framework — unit and e2e same syntax, seed-based graph testing, debugger infrastructure

- New crate el-test: test discovery, in-memory graph seeding, assertion evaluator, TestRunner, TestReport with human/JSON/JUnit XML output
- New keywords: test, seed, assert, target — fully integrated into lexer, parser, codegen, type-checker
- Parser extensions: TestDef, SeedStmt, Assert AST nodes; seed blocks handle type: as field name (keyword-as-ident in seed context)
- Debugger: DebugEvent, Debugger, StepMode, StackFrame in el-compiler — breakpoints, step-over, step-into, step-out
- CLI: el test-file <file.el> runs tests; el test integrates with project; el debug attaches debugger; --output json|junit for CI
- 52 new tests in el-test covering discovery, graph seeding, assertion evaluation, pass/fail/error/skip, report generation, JUnit XML
- Example: examples/hello-project/src/tests.el — 6 unit tests pass, 1 e2e test correctly skipped without ENGRAM_URL

Cargo.lock

@@ -294,6 +294,7 @@ dependencies = [
  "el-parser",
  "el-registry",
  "el-seal",
+ "el-test",
  "el-types",
  "thiserror 2.0.18",
  "tokio",
@@ -385,6 +386,19 @@ dependencies = [
  "thiserror 2.0.18",
 ]
 
+[[package]]
+name = "el-test"
+version = "0.1.0"
+dependencies = [
+ "el-compiler",
+ "el-lexer",
+ "el-parser",
+ "el-types",
+ "serde",
+ "serde_json",
+ "thiserror 2.0.18",
+]
+
 [[package]]
 name = "el-types"
 version = "0.1.0"