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/manifest.el

@@ -0,0 +1,9 @@
+package "nlg" {
+    version "0.1.0"
+    description "Native El natural language generation - vocabulary, grammar, realizer, morphology"
+    edition "2026"
+}
+
+build {
+    entry "src/nlg.el"
+}