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.toml

@@ -8,6 +8,7 @@ members = [
     "crates/el-manifest",
     "crates/el-registry",
     "crates/el-build",
+    "crates/el-test",
     "bin/el",
 ]
 resolver = "2"
@@ -28,6 +29,7 @@ el-seal     = { path = "crates/el-seal" }
 el-manifest = { path = "crates/el-manifest" }
 el-registry = { path = "crates/el-registry" }
 el-build    = { path = "crates/el-build" }
+el-test     = { path = "crates/el-test" }
 
 # Engram crypto (path dep — the sealed target depends on it)
 engram-crypto = { path = "../engram/crates/engram-crypto" }