elp(multilingual): native-el language layer — detect + localized phrases

Phase 3 piece 2. Ports multilingual.py: deterministic language detection
(en/es/pt/it) via stopword + diacritic scoring, localized fixed phrases (SACRED
per-language yes/no/decline/identity), PT/ES->EN retrieval term lexicon, and
EN->target predicate translation. No generative model.

Gate (multilingual_gate.el): 4/4 languages detected correctly; localized
declines + term/pred lexicons verified. Built bounded (elc rc=0 peak 25MB).

Worked through the documented el '+' mis-compile (two chained function-call Int
operands compile as string concat -> corrupt Int -> segfault on the accented
path); fixed by binding each score to an Int var and adding vars singly.

Simplifications (honest): diacritics scored by PRESENCE (str_contains) not
codepoint count (UTF-8 index safety); confidence scalar and the regex-based
parse_directive() from the reference not yet ported (directive parsing deferred
to the dialogue layer).

elp/manifest.el

@@ -82,6 +82,7 @@ build {
         "src/semantics.el",
         "src/comprehend.el",
         "src/propositions.el",
+        "src/multilingual.el",
         "src/elp.el",
     ]
 }