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/plural-noun.el

@@ -0,0 +1,16 @@
+// plural-noun.el - Test noun pluralization.
+//
+// Expected: "cats|children|boxes|cities|fish|leaves"
+
+fn run_test() -> String {
+    let r: [String] = native_list_empty()
+    let r = native_list_append(r, pluralize("cat"))
+    let r = native_list_append(r, pluralize("child"))
+    let r = native_list_append(r, pluralize("box"))
+    let r = native_list_append(r, pluralize("city"))
+    let r = native_list_append(r, pluralize("fish"))
+    let r = native_list_append(r, pluralize("leaf"))
+    return str_join(r, "|")
+}
+
+println(run_test())