feat: modelo Log y CRUD en fn_operations

Tipo Log con niveles debug/info/warn/error, source, entity_id y execution_id
opcionales. Migración 003_logs.sql y funciones InsertLog, GetLog, ListLogs
con filtros combinables.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fn_operations/migrations/003_logs.sql

@@ -0,0 +1,14 @@
+CREATE TABLE logs (
+	id           TEXT PRIMARY KEY,
+	level        TEXT NOT NULL DEFAULT 'info' CHECK(level IN ('debug','info','warn','error')),
+	source       TEXT NOT NULL DEFAULT '',
+	entity_id    TEXT NOT NULL DEFAULT '',
+	execution_id TEXT NOT NULL DEFAULT '',
+	message      TEXT NOT NULL,
+	metadata     TEXT NOT NULL DEFAULT '{}',
+	created_at   TEXT NOT NULL
+);
+
+CREATE INDEX idx_logs_level ON logs(level);
+CREATE INDEX idx_logs_source ON logs(source);
+CREATE INDEX idx_logs_created_at ON logs(created_at);