Add native El NLG system: morphology, vocabulary, grammar, realizer

Implements a complete natural language generation stack in El:
- morphology.el: English pluralization, verb conjugation (40+ irregulars), determiner agreement
- vocabulary.el: inline seed lexicon (~100 entries: pronouns, nouns, verbs, adjectives, etc.)
- grammar.el: CFG rules (S/NP/VP/PP), slot-map driven tree generator, s-expression renderer
- realizer.el: semantic form -> English text with tense/aspect/agreement, do-support for questions
- nlg.el: JSON-driven public API tying all modules together
- tests/run.sh: acceptance corpus runner (6 tests, all passing)

elp/tests/examples/verb-conjugation.el

@@ -0,0 +1,15 @@
+// verb-conjugation.el - Test verb conjugation.
+//
+// Expected: "ran|walked|is|am|sleeping"
+
+fn run_test() -> String {
+    let r: [String] = native_list_empty()
+    let r = native_list_append(r, verb_form("run",  "past",    "third",  "singular"))
+    let r = native_list_append(r, verb_form("walk", "past",    "third",  "singular"))
+    let r = native_list_append(r, verb_form("be",   "present", "third",  "singular"))
+    let r = native_list_append(r, verb_form("be",   "present", "first",  "singular"))
+    let r = native_list_append(r, verb_form("sleep","progressive","third","singular"))
+    return str_join(r, "|")
+}
+
+println(run_test())